diff --git a/.php_cs b/.php_cs
index e1343300..b16a35e5 100644
--- a/.php_cs
+++ b/.php_cs
@@ -32,7 +32,7 @@ return PhpCsFixer\Config::create()
         'no_blank_lines_after_class_opening' => true,
         'no_blank_lines_after_phpdoc' => true,
         'no_blank_lines_between_uses' => true,
-        'no_duplicate_semicolons' => true,
+        'no_empty_statement' => true,
         'no_extra_consecutive_blank_lines' => true,
         'no_leading_import_slash' => true,
         'no_leading_namespace_whitespace' => true,
diff --git a/composer.json b/composer.json
index 4d9aa733..1a6c609c 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^5.3",
-        "graylog2/gelf-php": "^1.0.1",
+        "graylog2/gelf-php": "1.3.x-dev",
         "sentry/sentry": "^0.13",
         "ruflin/elastica": ">=0.90 <3.0",
         "doctrine/couchdb": "~1.0@dev",
diff --git a/src/Monolog/DateTimeImmutable.php b/src/Monolog/DateTimeImmutable.php
index f1536f43..6ca786c1 100644
--- a/src/Monolog/DateTimeImmutable.php
+++ b/src/Monolog/DateTimeImmutable.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -23,11 +23,13 @@ class DateTimeImmutable extends \DateTimeImmutable implements \JsonSerializable
 
     public function __construct($useMicroseconds, \DateTimeZone $timezone = null)
     {
-        $date = null;
+        $date = 'now';
         if ($useMicroseconds) {
+            // Circumvent DateTimeImmutable::createFromFormat() which always returns \DateTimeImmutable instead of `static`
+            // @link https://bugs.php.net/bug.php?id=60302
             $timestamp = microtime(true);
             $microseconds = sprintf("%06d", ($timestamp - floor($timestamp)) * 1000000);
-            $date = date('Y-m-d H:i:s.' . $microseconds, $timestamp);
+            $date = date('Y-m-d H:i:s.' . $microseconds, (int) $timestamp);
         }
         parent::__construct($date, $timezone);
 
diff --git a/src/Monolog/ErrorHandler.php b/src/Monolog/ErrorHandler.php
index 5a89939c..aaf2d9bd 100644
--- a/src/Monolog/ErrorHandler.php
+++ b/src/Monolog/ErrorHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/ChromePHPFormatter.php b/src/Monolog/Formatter/ChromePHPFormatter.php
index 0fda87a4..12b0d60d 100644
--- a/src/Monolog/Formatter/ChromePHPFormatter.php
+++ b/src/Monolog/Formatter/ChromePHPFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/ElasticaFormatter.php b/src/Monolog/Formatter/ElasticaFormatter.php
index 4c556cf1..e6a5e67c 100644
--- a/src/Monolog/Formatter/ElasticaFormatter.php
+++ b/src/Monolog/Formatter/ElasticaFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/FlowdockFormatter.php b/src/Monolog/Formatter/FlowdockFormatter.php
index 2d750792..6a33038f 100644
--- a/src/Monolog/Formatter/FlowdockFormatter.php
+++ b/src/Monolog/Formatter/FlowdockFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/FluentdFormatter.php b/src/Monolog/Formatter/FluentdFormatter.php
index 5ce2aca3..e2a66585 100644
--- a/src/Monolog/Formatter/FluentdFormatter.php
+++ b/src/Monolog/Formatter/FluentdFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/FormatterInterface.php b/src/Monolog/Formatter/FormatterInterface.php
index b5de7511..7442134e 100644
--- a/src/Monolog/Formatter/FormatterInterface.php
+++ b/src/Monolog/Formatter/FormatterInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/GelfMessageFormatter.php b/src/Monolog/Formatter/GelfMessageFormatter.php
index 847773f5..047358a1 100644
--- a/src/Monolog/Formatter/GelfMessageFormatter.php
+++ b/src/Monolog/Formatter/GelfMessageFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -68,7 +68,12 @@ class GelfMessageFormatter extends NormalizerFormatter
      */
     public function format(array $record)
     {
-        $record = parent::format($record);
+        if (isset($record['context'])) {
+            $record['context'] = parent::format($record['context']);
+        }
+        if (isset($record['extra'])) {
+            $record['extra'] = parent::format($record['extra']);
+        }
 
         if (!isset($record['datetime'], $record['message'], $record['level'])) {
             throw new \InvalidArgumentException('The record should at least contain datetime, message and level keys, '.var_export($record, true).' given');
diff --git a/src/Monolog/Formatter/HtmlFormatter.php b/src/Monolog/Formatter/HtmlFormatter.php
index 7b2d3f67..19058918 100644
--- a/src/Monolog/Formatter/HtmlFormatter.php
+++ b/src/Monolog/Formatter/HtmlFormatter.php
@@ -1,4 +1,5 @@
-<?php
+<?php declare(strict_types=1);
+
 /*
  * This file is part of the Monolog package.
  *
@@ -87,7 +88,7 @@ class HtmlFormatter extends NormalizerFormatter
         $output .= '<table cellspacing="1" width="100%" class="monolog-output">';
 
         $output .= $this->addRow('Message', (string) $record['message']);
-        $output .= $this->addRow('Time', $record['datetime']->format($this->dateFormat));
+        $output .= $this->addRow('Time', $this->formatDate($record['datetime']));
         $output .= $this->addRow('Channel', $record['channel']);
         if ($record['context']) {
             $embeddedTable = '<table cellspacing="1" width="100%">';
diff --git a/src/Monolog/Formatter/JsonFormatter.php b/src/Monolog/Formatter/JsonFormatter.php
index 17ede7da..2c7db92f 100644
--- a/src/Monolog/Formatter/JsonFormatter.php
+++ b/src/Monolog/Formatter/JsonFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/LineFormatter.php b/src/Monolog/Formatter/LineFormatter.php
index 7a94a7f3..5a65b4c0 100644
--- a/src/Monolog/Formatter/LineFormatter.php
+++ b/src/Monolog/Formatter/LineFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/LogglyFormatter.php b/src/Monolog/Formatter/LogglyFormatter.php
index aa1ff809..d4190df3 100644
--- a/src/Monolog/Formatter/LogglyFormatter.php
+++ b/src/Monolog/Formatter/LogglyFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/LogstashFormatter.php b/src/Monolog/Formatter/LogstashFormatter.php
index de456cfb..31e354c0 100644
--- a/src/Monolog/Formatter/LogstashFormatter.php
+++ b/src/Monolog/Formatter/LogstashFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/MongoDBFormatter.php b/src/Monolog/Formatter/MongoDBFormatter.php
index e58cb7e0..6d9456be 100644
--- a/src/Monolog/Formatter/MongoDBFormatter.php
+++ b/src/Monolog/Formatter/MongoDBFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/NormalizerFormatter.php b/src/Monolog/Formatter/NormalizerFormatter.php
index 8c060b1b..50c3299b 100644
--- a/src/Monolog/Formatter/NormalizerFormatter.php
+++ b/src/Monolog/Formatter/NormalizerFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -30,7 +30,7 @@ class NormalizerFormatter implements FormatterInterface
      */
     public function __construct(string $dateFormat = null)
     {
-        $this->dateFormat = $dateFormat;
+        $this->dateFormat = null === $dateFormat ? static::SIMPLE_DATE : $dateFormat;
         if (!function_exists('json_encode')) {
             throw new \RuntimeException('PHP\'s json extension is required to use Monolog\'s NormalizerFormatter');
         }
@@ -87,11 +87,7 @@ class NormalizerFormatter implements FormatterInterface
         }
 
         if ($data instanceof \DateTimeInterface) {
-            if ($data instanceof DateTimeImmutable) {
-                return (string) $data;
-            }
-
-            return $data->format($this->dateFormat ?: static::SIMPLE_DATE);
+            return $this->formatDate($data);
         }
 
         if (is_object($data)) {
@@ -271,7 +267,9 @@ class NormalizerFormatter implements FormatterInterface
         if (is_string($data) && !preg_match('//u', $data)) {
             $data = preg_replace_callback(
                 '/[\x80-\xFF]+/',
-                function ($m) { return utf8_encode($m[0]); },
+                function ($m) {
+                    return utf8_encode($m[0]);
+                },
                 $data
             );
             $data = str_replace(
@@ -281,4 +279,13 @@ class NormalizerFormatter implements FormatterInterface
             );
         }
     }
+
+    protected function formatDate(\DateTimeInterface $date)
+    {
+        if ($date instanceof DateTimeImmutable) {
+            return (string) $date;
+        }
+
+        return $date->format($this->dateFormat);
+    }
 }
diff --git a/src/Monolog/Formatter/ScalarFormatter.php b/src/Monolog/Formatter/ScalarFormatter.php
index 5d345d53..fcff1294 100644
--- a/src/Monolog/Formatter/ScalarFormatter.php
+++ b/src/Monolog/Formatter/ScalarFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Formatter/WildfireFormatter.php b/src/Monolog/Formatter/WildfireFormatter.php
index 4a2f1cb1..3c7aea58 100644
--- a/src/Monolog/Formatter/WildfireFormatter.php
+++ b/src/Monolog/Formatter/WildfireFormatter.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/AbstractHandler.php b/src/Monolog/Handler/AbstractHandler.php
index ef6015e2..ea79ec92 100644
--- a/src/Monolog/Handler/AbstractHandler.php
+++ b/src/Monolog/Handler/AbstractHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/AbstractProcessingHandler.php b/src/Monolog/Handler/AbstractProcessingHandler.php
index 49a92483..654e6718 100644
--- a/src/Monolog/Handler/AbstractProcessingHandler.php
+++ b/src/Monolog/Handler/AbstractProcessingHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/AbstractSyslogHandler.php b/src/Monolog/Handler/AbstractSyslogHandler.php
index 24d8219b..d6fc41ef 100644
--- a/src/Monolog/Handler/AbstractSyslogHandler.php
+++ b/src/Monolog/Handler/AbstractSyslogHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -83,7 +83,7 @@ abstract class AbstractSyslogHandler extends AbstractProcessingHandler
         }
 
         // convert textual description of facility to syslog constant
-        if (array_key_exists(strtolower($facility), $this->facilities)) {
+        if (is_string($facility) && array_key_exists(strtolower($facility), $this->facilities)) {
             $facility = $this->facilities[strtolower($facility)];
         } elseif (!in_array($facility, array_values($this->facilities), true)) {
             throw new \UnexpectedValueException('Unknown facility value "'.$facility.'" given');
diff --git a/src/Monolog/Handler/AmqpHandler.php b/src/Monolog/Handler/AmqpHandler.php
index 223d6bf5..5b77e4f7 100644
--- a/src/Monolog/Handler/AmqpHandler.php
+++ b/src/Monolog/Handler/AmqpHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/BrowserConsoleHandler.php b/src/Monolog/Handler/BrowserConsoleHandler.php
index 59636f2b..4879d24d 100644
--- a/src/Monolog/Handler/BrowserConsoleHandler.php
+++ b/src/Monolog/Handler/BrowserConsoleHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/BufferHandler.php b/src/Monolog/Handler/BufferHandler.php
index e65121cf..5ce6c396 100644
--- a/src/Monolog/Handler/BufferHandler.php
+++ b/src/Monolog/Handler/BufferHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/ChromePHPHandler.php b/src/Monolog/Handler/ChromePHPHandler.php
index 758ec898..31573adf 100644
--- a/src/Monolog/Handler/ChromePHPHandler.php
+++ b/src/Monolog/Handler/ChromePHPHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/CouchDBHandler.php b/src/Monolog/Handler/CouchDBHandler.php
index 4540e2c5..e0603f34 100644
--- a/src/Monolog/Handler/CouchDBHandler.php
+++ b/src/Monolog/Handler/CouchDBHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -58,7 +58,7 @@ class CouchDBHandler extends AbstractProcessingHandler
             ],
         ]);
 
-        if (false === @file_get_contents($url, null, $context)) {
+        if (false === @file_get_contents($url, false, $context)) {
             throw new \RuntimeException(sprintf('Could not connect to %s', $url));
         }
     }
diff --git a/src/Monolog/Handler/CubeHandler.php b/src/Monolog/Handler/CubeHandler.php
index 7d831fef..ab6e007e 100644
--- a/src/Monolog/Handler/CubeHandler.php
+++ b/src/Monolog/Handler/CubeHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/Curl/Util.php b/src/Monolog/Handler/Curl/Util.php
index 2ca774d8..b0bec3d9 100644
--- a/src/Monolog/Handler/Curl/Util.php
+++ b/src/Monolog/Handler/Curl/Util.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/DeduplicationHandler.php b/src/Monolog/Handler/DeduplicationHandler.php
index 5d95585e..235b3b85 100644
--- a/src/Monolog/Handler/DeduplicationHandler.php
+++ b/src/Monolog/Handler/DeduplicationHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -144,7 +144,7 @@ class DeduplicationHandler extends BufferHandler
 
         while (!feof($handle)) {
             $log = fgets($handle);
-            if (substr($log, 0, 10) >= $timestampValidity) {
+            if ($log && substr($log, 0, 10) >= $timestampValidity) {
                 $validLogs[] = $log;
             }
         }
diff --git a/src/Monolog/Handler/DoctrineCouchDBHandler.php b/src/Monolog/Handler/DoctrineCouchDBHandler.php
index 2752dd2f..13a08eec 100644
--- a/src/Monolog/Handler/DoctrineCouchDBHandler.php
+++ b/src/Monolog/Handler/DoctrineCouchDBHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/DynamoDbHandler.php b/src/Monolog/Handler/DynamoDbHandler.php
index 24139248..43d4ddb7 100644
--- a/src/Monolog/Handler/DynamoDbHandler.php
+++ b/src/Monolog/Handler/DynamoDbHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/ElasticSearchHandler.php b/src/Monolog/Handler/ElasticSearchHandler.php
index 64a0b41c..fbb999fd 100644
--- a/src/Monolog/Handler/ElasticSearchHandler.php
+++ b/src/Monolog/Handler/ElasticSearchHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/ErrorLogHandler.php b/src/Monolog/Handler/ErrorLogHandler.php
index fc89fcde..b2728781 100644
--- a/src/Monolog/Handler/ErrorLogHandler.php
+++ b/src/Monolog/Handler/ErrorLogHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FilterHandler.php b/src/Monolog/Handler/FilterHandler.php
index ff1a13d7..da0634a7 100644
--- a/src/Monolog/Handler/FilterHandler.php
+++ b/src/Monolog/Handler/FilterHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FingersCrossed/ActivationStrategyInterface.php b/src/Monolog/Handler/FingersCrossed/ActivationStrategyInterface.php
index c3e42efe..f9cab618 100644
--- a/src/Monolog/Handler/FingersCrossed/ActivationStrategyInterface.php
+++ b/src/Monolog/Handler/FingersCrossed/ActivationStrategyInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FingersCrossed/ChannelLevelActivationStrategy.php b/src/Monolog/Handler/FingersCrossed/ChannelLevelActivationStrategy.php
index 3f599656..63a14cb6 100644
--- a/src/Monolog/Handler/FingersCrossed/ChannelLevelActivationStrategy.php
+++ b/src/Monolog/Handler/FingersCrossed/ChannelLevelActivationStrategy.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FingersCrossed/ErrorLevelActivationStrategy.php b/src/Monolog/Handler/FingersCrossed/ErrorLevelActivationStrategy.php
index 6e630852..d0ebd840 100644
--- a/src/Monolog/Handler/FingersCrossed/ErrorLevelActivationStrategy.php
+++ b/src/Monolog/Handler/FingersCrossed/ErrorLevelActivationStrategy.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FingersCrossedHandler.php b/src/Monolog/Handler/FingersCrossedHandler.php
index 1991acf7..f0151d1e 100644
--- a/src/Monolog/Handler/FingersCrossedHandler.php
+++ b/src/Monolog/Handler/FingersCrossedHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FirePHPHandler.php b/src/Monolog/Handler/FirePHPHandler.php
index a6bc6cf7..42c78f65 100644
--- a/src/Monolog/Handler/FirePHPHandler.php
+++ b/src/Monolog/Handler/FirePHPHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FleepHookHandler.php b/src/Monolog/Handler/FleepHookHandler.php
index 964f5f78..748100b1 100644
--- a/src/Monolog/Handler/FleepHookHandler.php
+++ b/src/Monolog/Handler/FleepHookHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FlowdockHandler.php b/src/Monolog/Handler/FlowdockHandler.php
index 2f2c3c7c..b3fc9b41 100644
--- a/src/Monolog/Handler/FlowdockHandler.php
+++ b/src/Monolog/Handler/FlowdockHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FormattableHandlerInterface.php b/src/Monolog/Handler/FormattableHandlerInterface.php
index a633dece..fc1693cd 100644
--- a/src/Monolog/Handler/FormattableHandlerInterface.php
+++ b/src/Monolog/Handler/FormattableHandlerInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/FormattableHandlerTrait.php b/src/Monolog/Handler/FormattableHandlerTrait.php
index 500a071e..2b7e56f9 100644
--- a/src/Monolog/Handler/FormattableHandlerTrait.php
+++ b/src/Monolog/Handler/FormattableHandlerTrait.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/GelfHandler.php b/src/Monolog/Handler/GelfHandler.php
index 222a895b..4a6c0f8d 100644
--- a/src/Monolog/Handler/GelfHandler.php
+++ b/src/Monolog/Handler/GelfHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/GroupHandler.php b/src/Monolog/Handler/GroupHandler.php
index 193465fd..a6f063c8 100644
--- a/src/Monolog/Handler/GroupHandler.php
+++ b/src/Monolog/Handler/GroupHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/Handler.php b/src/Monolog/Handler/Handler.php
index 6d1e7bfc..347e7b70 100644
--- a/src/Monolog/Handler/Handler.php
+++ b/src/Monolog/Handler/Handler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/HandlerInterface.php b/src/Monolog/Handler/HandlerInterface.php
index 7f8ffbe9..472fd31b 100644
--- a/src/Monolog/Handler/HandlerInterface.php
+++ b/src/Monolog/Handler/HandlerInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/HandlerWrapper.php b/src/Monolog/Handler/HandlerWrapper.php
index f79642fd..5eacf003 100644
--- a/src/Monolog/Handler/HandlerWrapper.php
+++ b/src/Monolog/Handler/HandlerWrapper.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/HipChatHandler.php b/src/Monolog/Handler/HipChatHandler.php
index 8e7ab65a..98441f3e 100644
--- a/src/Monolog/Handler/HipChatHandler.php
+++ b/src/Monolog/Handler/HipChatHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/IFTTTHandler.php b/src/Monolog/Handler/IFTTTHandler.php
index f4dbf681..46792ee4 100644
--- a/src/Monolog/Handler/IFTTTHandler.php
+++ b/src/Monolog/Handler/IFTTTHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/LogEntriesHandler.php b/src/Monolog/Handler/LogEntriesHandler.php
index 494c605b..c74b9d2e 100644
--- a/src/Monolog/Handler/LogEntriesHandler.php
+++ b/src/Monolog/Handler/LogEntriesHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/LogglyHandler.php b/src/Monolog/Handler/LogglyHandler.php
index 874cf70a..544e7c7f 100644
--- a/src/Monolog/Handler/LogglyHandler.php
+++ b/src/Monolog/Handler/LogglyHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/MailHandler.php b/src/Monolog/Handler/MailHandler.php
index 2b9d74c8..634fbc19 100644
--- a/src/Monolog/Handler/MailHandler.php
+++ b/src/Monolog/Handler/MailHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -46,7 +46,7 @@ abstract class MailHandler extends AbstractProcessingHandler
      * @param string $content formatted email body to be sent
      * @param array  $records the array of log records that formed this content
      */
-    abstract protected function send($content, array $records);
+    abstract protected function send(string $content, array $records);
 
     /**
      * {@inheritdoc}
diff --git a/src/Monolog/Handler/MandrillHandler.php b/src/Monolog/Handler/MandrillHandler.php
index 1fb9dc6a..68ec5682 100644
--- a/src/Monolog/Handler/MandrillHandler.php
+++ b/src/Monolog/Handler/MandrillHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/MissingExtensionException.php b/src/Monolog/Handler/MissingExtensionException.php
index 4724a7e2..1554b345 100644
--- a/src/Monolog/Handler/MissingExtensionException.php
+++ b/src/Monolog/Handler/MissingExtensionException.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/MongoDBHandler.php b/src/Monolog/Handler/MongoDBHandler.php
index d6ca24c9..f302d312 100644
--- a/src/Monolog/Handler/MongoDBHandler.php
+++ b/src/Monolog/Handler/MongoDBHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/NativeMailerHandler.php b/src/Monolog/Handler/NativeMailerHandler.php
index 4289e35e..b597761e 100644
--- a/src/Monolog/Handler/NativeMailerHandler.php
+++ b/src/Monolog/Handler/NativeMailerHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -115,7 +115,7 @@ class NativeMailerHandler extends MailHandler
     /**
      * {@inheritdoc}
      */
-    protected function send($content, array $records)
+    protected function send(string $content, array $records)
     {
         $contentType = $this->getContentType() ?: ($this->isHtmlBody($content) ? 'text/html' : 'text/plain');
 
diff --git a/src/Monolog/Handler/NewRelicHandler.php b/src/Monolog/Handler/NewRelicHandler.php
index 03952e77..fb037782 100644
--- a/src/Monolog/Handler/NewRelicHandler.php
+++ b/src/Monolog/Handler/NewRelicHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/NullHandler.php b/src/Monolog/Handler/NullHandler.php
index 3179d394..93678e8f 100644
--- a/src/Monolog/Handler/NullHandler.php
+++ b/src/Monolog/Handler/NullHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/PHPConsoleHandler.php b/src/Monolog/Handler/PHPConsoleHandler.php
index 10466ad4..7807a6f2 100644
--- a/src/Monolog/Handler/PHPConsoleHandler.php
+++ b/src/Monolog/Handler/PHPConsoleHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/ProcessHandler.php b/src/Monolog/Handler/ProcessHandler.php
index 4c2d0054..9c135f87 100644
--- a/src/Monolog/Handler/ProcessHandler.php
+++ b/src/Monolog/Handler/ProcessHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/ProcessableHandlerInterface.php b/src/Monolog/Handler/ProcessableHandlerInterface.php
index 3943967e..59ec9820 100644
--- a/src/Monolog/Handler/ProcessableHandlerInterface.php
+++ b/src/Monolog/Handler/ProcessableHandlerInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/ProcessableHandlerTrait.php b/src/Monolog/Handler/ProcessableHandlerTrait.php
index 974f1af3..d28d46bb 100644
--- a/src/Monolog/Handler/ProcessableHandlerTrait.php
+++ b/src/Monolog/Handler/ProcessableHandlerTrait.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/PsrHandler.php b/src/Monolog/Handler/PsrHandler.php
index 2d613021..415b45f0 100644
--- a/src/Monolog/Handler/PsrHandler.php
+++ b/src/Monolog/Handler/PsrHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/PushoverHandler.php b/src/Monolog/Handler/PushoverHandler.php
index aceff256..b53ce6c1 100644
--- a/src/Monolog/Handler/PushoverHandler.php
+++ b/src/Monolog/Handler/PushoverHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/RavenHandler.php b/src/Monolog/Handler/RavenHandler.php
index a573819c..db64f803 100644
--- a/src/Monolog/Handler/RavenHandler.php
+++ b/src/Monolog/Handler/RavenHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/RedisHandler.php b/src/Monolog/Handler/RedisHandler.php
index e39c2b34..f77d4fda 100644
--- a/src/Monolog/Handler/RedisHandler.php
+++ b/src/Monolog/Handler/RedisHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/RollbarHandler.php b/src/Monolog/Handler/RollbarHandler.php
index 572c40ba..0a82faa5 100644
--- a/src/Monolog/Handler/RollbarHandler.php
+++ b/src/Monolog/Handler/RollbarHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/RotatingFileHandler.php b/src/Monolog/Handler/RotatingFileHandler.php
index ade59411..8c99f2d5 100644
--- a/src/Monolog/Handler/RotatingFileHandler.php
+++ b/src/Monolog/Handler/RotatingFileHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -134,7 +134,8 @@ class RotatingFileHandler extends StreamHandler
             if (is_writable($file)) {
                 // suppress errors here as unlink() might fail if two processes
                 // are cleaning up/rotating at the same time
-                set_error_handler(function ($errno, $errstr, $errfile, $errline) {});
+                set_error_handler(function ($errno, $errstr, $errfile, $errline) {
+                });
                 unlink($file);
                 restore_error_handler();
             }
diff --git a/src/Monolog/Handler/SamplingHandler.php b/src/Monolog/Handler/SamplingHandler.php
index a0b784b2..8a25cbb7 100644
--- a/src/Monolog/Handler/SamplingHandler.php
+++ b/src/Monolog/Handler/SamplingHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/SendGridHandler.php b/src/Monolog/Handler/SendGridHandler.php
index cee69861..3a91cb41 100644
--- a/src/Monolog/Handler/SendGridHandler.php
+++ b/src/Monolog/Handler/SendGridHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/SlackHandler.php b/src/Monolog/Handler/SlackHandler.php
index 35c809a2..a5db721d 100644
--- a/src/Monolog/Handler/SlackHandler.php
+++ b/src/Monolog/Handler/SlackHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -92,7 +92,7 @@ class SlackHandler extends SocketHandler
         $this->token = $token;
         $this->channel = $channel;
         $this->username = $username;
-        $this->iconEmoji = trim($iconEmoji, ':');
+        $this->iconEmoji = is_string($iconEmoji) ? trim($iconEmoji, ':') : null;
         $this->useAttachment = $useAttachment;
         $this->useShortAttachment = $useShortAttachment;
         $this->includeContextAndExtra = $includeContextAndExtra;
diff --git a/src/Monolog/Handler/SocketHandler.php b/src/Monolog/Handler/SocketHandler.php
index 7a61bf4e..520bedd5 100644
--- a/src/Monolog/Handler/SocketHandler.php
+++ b/src/Monolog/Handler/SocketHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/StreamHandler.php b/src/Monolog/Handler/StreamHandler.php
index 8936e67f..4a7433c0 100644
--- a/src/Monolog/Handler/StreamHandler.php
+++ b/src/Monolog/Handler/StreamHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/SwiftMailerHandler.php b/src/Monolog/Handler/SwiftMailerHandler.php
index 44026fc3..549246d9 100644
--- a/src/Monolog/Handler/SwiftMailerHandler.php
+++ b/src/Monolog/Handler/SwiftMailerHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -13,6 +13,7 @@ namespace Monolog\Handler;
 
 use Monolog\Logger;
 use Monolog\Formatter\LineFormatter;
+use Swift_Message;
 
 /**
  * SwiftMailerHandler uses Swift_Mailer to send the emails
@@ -26,7 +27,7 @@ class SwiftMailerHandler extends MailHandler
 
     /**
      * @param \Swift_Mailer           $mailer  The mailer to use
-     * @param callable|\Swift_Message $message An example message for real messages, only the body will be replaced
+     * @param callable|Swift_Message $message An example message for real messages, only the body will be replaced
      * @param int                     $level   The minimum logging level at which this handler will be triggered
      * @param Boolean                 $bubble  Whether the messages that are handled can bubble up the stack or not
      */
@@ -41,7 +42,7 @@ class SwiftMailerHandler extends MailHandler
     /**
      * {@inheritdoc}
      */
-    protected function send($content, array $records)
+    protected function send(string $content, array $records)
     {
         $this->mailer->send($this->buildMessage($content, $records));
     }
@@ -51,19 +52,19 @@ class SwiftMailerHandler extends MailHandler
      *
      * @param  string         $content formatted email body to be sent
      * @param  array          $records Log records that formed the content
-     * @return \Swift_Message
+     * @return Swift_Message
      */
-    protected function buildMessage($content, array $records)
+    protected function buildMessage(string $content, array $records): Swift_Message
     {
         $message = null;
-        if ($this->messageTemplate instanceof \Swift_Message) {
+        if ($this->messageTemplate instanceof Swift_Message) {
             $message = clone $this->messageTemplate;
             $message->generateId();
         } elseif (is_callable($this->messageTemplate)) {
             $message = call_user_func($this->messageTemplate, $content, $records);
         }
 
-        if (!$message instanceof \Swift_Message) {
+        if (!$message instanceof Swift_Message) {
             throw new \InvalidArgumentException('Could not resolve message as instance of Swift_Message or a callable returning it');
         }
 
diff --git a/src/Monolog/Handler/SyslogHandler.php b/src/Monolog/Handler/SyslogHandler.php
index 376bc3b2..863fc56d 100644
--- a/src/Monolog/Handler/SyslogHandler.php
+++ b/src/Monolog/Handler/SyslogHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/SyslogUdp/UdpSocket.php b/src/Monolog/Handler/SyslogUdp/UdpSocket.php
index 3bff085b..f54ac4e8 100644
--- a/src/Monolog/Handler/SyslogUdp/UdpSocket.php
+++ b/src/Monolog/Handler/SyslogUdp/UdpSocket.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/SyslogUdpHandler.php b/src/Monolog/Handler/SyslogUdpHandler.php
index b175cc3a..4e2335d8 100644
--- a/src/Monolog/Handler/SyslogUdpHandler.php
+++ b/src/Monolog/Handler/SyslogUdpHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/TestHandler.php b/src/Monolog/Handler/TestHandler.php
index b34ebaa8..db63565e 100644
--- a/src/Monolog/Handler/TestHandler.php
+++ b/src/Monolog/Handler/TestHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/WhatFailureGroupHandler.php b/src/Monolog/Handler/WhatFailureGroupHandler.php
index 6dbfa812..42c2336a 100644
--- a/src/Monolog/Handler/WhatFailureGroupHandler.php
+++ b/src/Monolog/Handler/WhatFailureGroupHandler.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Handler/ZendMonitorHandler.php b/src/Monolog/Handler/ZendMonitorHandler.php
index 6d771226..c0bceb42 100644
--- a/src/Monolog/Handler/ZendMonitorHandler.php
+++ b/src/Monolog/Handler/ZendMonitorHandler.php
@@ -1,4 +1,5 @@
-<?php
+<?php declare(strict_types=1);
+
 /*
  * This file is part of the Monolog package.
  *
diff --git a/src/Monolog/Logger.php b/src/Monolog/Logger.php
index 3016ba55..3878f596 100644
--- a/src/Monolog/Logger.php
+++ b/src/Monolog/Logger.php
@@ -1,15 +1,4 @@
-<?php
-
-/*
- * This file is part of the Monolog package.
- *
- * (c) Jordi Boggiano <j.boggiano@seld.be>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-declare(strict_types=1);
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -173,7 +162,7 @@ class Logger implements LoggerInterface
      *
      * @return static
      */
-    public function withName($name)
+    public function withName(string $name): self
     {
         $new = clone $this;
         $new->name = $name;
@@ -315,7 +304,8 @@ class Logger implements LoggerInterface
             return false;
         }
 
-        $ts = $this->createDateTime();
+        $dateTime = new DateTimeImmutable($this->microsecondTimestamps, $this->timezone);
+        $dateTime->setTimezone($this->timezone);
 
         $record = [
             'message' => $message,
@@ -323,7 +313,7 @@ class Logger implements LoggerInterface
             'level' => $level,
             'level_name' => $levelName,
             'channel' => $this->name,
-            'datetime' => $ts,
+            'datetime' => $dateTime,
             'extra' => [],
         ];
 
@@ -555,17 +545,4 @@ class Logger implements LoggerInterface
     {
         return $this->timezone;
     }
-
-    /**
-     * Circumvent DateTimeImmutable::createFromFormat() which always returns the native DateTime instead of the specialized one
-     *
-     * @link https://bugs.php.net/bug.php?id=60302
-     */
-    private function createDateTime(): DateTimeImmutable
-    {
-        $dateTime = new DateTimeImmutable($this->microsecondTimestamps, $this->timezone);
-        $dateTime->setTimezone($this->timezone);
-
-        return $dateTime;
-    }
 }
diff --git a/src/Monolog/Processor/GitProcessor.php b/src/Monolog/Processor/GitProcessor.php
index c4d95a91..cf16be8e 100644
--- a/src/Monolog/Processor/GitProcessor.php
+++ b/src/Monolog/Processor/GitProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/IntrospectionProcessor.php b/src/Monolog/Processor/IntrospectionProcessor.php
index bec43c32..59e2f481 100644
--- a/src/Monolog/Processor/IntrospectionProcessor.php
+++ b/src/Monolog/Processor/IntrospectionProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/MemoryPeakUsageProcessor.php b/src/Monolog/Processor/MemoryPeakUsageProcessor.php
index 0543e929..b8fd91ce 100644
--- a/src/Monolog/Processor/MemoryPeakUsageProcessor.php
+++ b/src/Monolog/Processor/MemoryPeakUsageProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/MemoryProcessor.php b/src/Monolog/Processor/MemoryProcessor.php
index 85f9dc5e..460caa6b 100644
--- a/src/Monolog/Processor/MemoryProcessor.php
+++ b/src/Monolog/Processor/MemoryProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/MemoryUsageProcessor.php b/src/Monolog/Processor/MemoryUsageProcessor.php
index 2783d656..cb6b2ea8 100644
--- a/src/Monolog/Processor/MemoryUsageProcessor.php
+++ b/src/Monolog/Processor/MemoryUsageProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/ProcessIdProcessor.php b/src/Monolog/Processor/ProcessIdProcessor.php
index 9d3f5590..7ddafea9 100644
--- a/src/Monolog/Processor/ProcessIdProcessor.php
+++ b/src/Monolog/Processor/ProcessIdProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/PsrLogMessageProcessor.php b/src/Monolog/Processor/PsrLogMessageProcessor.php
index fd907a19..e1a42cd0 100644
--- a/src/Monolog/Processor/PsrLogMessageProcessor.php
+++ b/src/Monolog/Processor/PsrLogMessageProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/TagProcessor.php b/src/Monolog/Processor/TagProcessor.php
index a5f1e7a8..19458e27 100644
--- a/src/Monolog/Processor/TagProcessor.php
+++ b/src/Monolog/Processor/TagProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/UidProcessor.php b/src/Monolog/Processor/UidProcessor.php
index 812707cd..891e9df7 100644
--- a/src/Monolog/Processor/UidProcessor.php
+++ b/src/Monolog/Processor/UidProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Processor/WebProcessor.php b/src/Monolog/Processor/WebProcessor.php
index 50e7ca34..91abeec9 100644
--- a/src/Monolog/Processor/WebProcessor.php
+++ b/src/Monolog/Processor/WebProcessor.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Registry.php b/src/Monolog/Registry.php
index 587ec16e..64612c8e 100644
--- a/src/Monolog/Registry.php
+++ b/src/Monolog/Registry.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/src/Monolog/Test/TestCase.php b/src/Monolog/Test/TestCase.php
index fab3deea..7cb7fbfa 100644
--- a/src/Monolog/Test/TestCase.php
+++ b/src/Monolog/Test/TestCase.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -59,7 +59,9 @@ class TestCase extends \PHPUnit_Framework_TestCase
         $formatter = $this->getMock('Monolog\\Formatter\\FormatterInterface');
         $formatter->expects($this->any())
             ->method('format')
-            ->will($this->returnCallback(function ($record) { return $record['message']; }));
+            ->will($this->returnCallback(function ($record) {
+                return $record['message'];
+            }));
 
         return $formatter;
     }
diff --git a/tests/Monolog/ErrorHandlerTest.php b/tests/Monolog/ErrorHandlerTest.php
index 26ac7ead..7b3ba82a 100644
--- a/tests/Monolog/ErrorHandlerTest.php
+++ b/tests/Monolog/ErrorHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/ChromePHPFormatterTest.php b/tests/Monolog/Formatter/ChromePHPFormatterTest.php
index a6bb96a1..08a8e1bd 100644
--- a/tests/Monolog/Formatter/ChromePHPFormatterTest.php
+++ b/tests/Monolog/Formatter/ChromePHPFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/ElasticaFormatterTest.php b/tests/Monolog/Formatter/ElasticaFormatterTest.php
index 17c43d5c..8e88e695 100644
--- a/tests/Monolog/Formatter/ElasticaFormatterTest.php
+++ b/tests/Monolog/Formatter/ElasticaFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/FlowdockFormatterTest.php b/tests/Monolog/Formatter/FlowdockFormatterTest.php
index cf5b416f..f922d530 100644
--- a/tests/Monolog/Formatter/FlowdockFormatterTest.php
+++ b/tests/Monolog/Formatter/FlowdockFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/FluentdFormatterTest.php b/tests/Monolog/Formatter/FluentdFormatterTest.php
index 828a3964..0be8d8f9 100644
--- a/tests/Monolog/Formatter/FluentdFormatterTest.php
+++ b/tests/Monolog/Formatter/FluentdFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/GelfMessageFormatterTest.php b/tests/Monolog/Formatter/GelfMessageFormatterTest.php
index 2b61387d..897aa81f 100644
--- a/tests/Monolog/Formatter/GelfMessageFormatterTest.php
+++ b/tests/Monolog/Formatter/GelfMessageFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -216,7 +216,7 @@ class GelfMessageFormatterTest extends \PHPUnit_Framework_TestCase
         $length = 200;
 
         foreach ($messageArray as $key => $value) {
-            if (!in_array($key, ['level', 'timestamp'])) {
+            if (!in_array($key, ['level', 'timestamp']) && is_string($value)) {
                 $length += strlen($value);
             }
         }
diff --git a/tests/Monolog/Formatter/JsonFormatterTest.php b/tests/Monolog/Formatter/JsonFormatterTest.php
index 2a0b8d17..392647fd 100644
--- a/tests/Monolog/Formatter/JsonFormatterTest.php
+++ b/tests/Monolog/Formatter/JsonFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/LineFormatterTest.php b/tests/Monolog/Formatter/LineFormatterTest.php
index efb90b61..cbbbc666 100644
--- a/tests/Monolog/Formatter/LineFormatterTest.php
+++ b/tests/Monolog/Formatter/LineFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/LogglyFormatterTest.php b/tests/Monolog/Formatter/LogglyFormatterTest.php
index ce5251b4..26d6fa18 100644
--- a/tests/Monolog/Formatter/LogglyFormatterTest.php
+++ b/tests/Monolog/Formatter/LogglyFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/LogstashFormatterTest.php b/tests/Monolog/Formatter/LogstashFormatterTest.php
index ed45100c..57d67592 100644
--- a/tests/Monolog/Formatter/LogstashFormatterTest.php
+++ b/tests/Monolog/Formatter/LogstashFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/MongoDBFormatterTest.php b/tests/Monolog/Formatter/MongoDBFormatterTest.php
index a66cedfe..2933497c 100644
--- a/tests/Monolog/Formatter/MongoDBFormatterTest.php
+++ b/tests/Monolog/Formatter/MongoDBFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/NormalizerFormatterTest.php b/tests/Monolog/Formatter/NormalizerFormatterTest.php
index 4d929c75..a3e0ef68 100644
--- a/tests/Monolog/Formatter/NormalizerFormatterTest.php
+++ b/tests/Monolog/Formatter/NormalizerFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -273,18 +273,14 @@ class NormalizerFormatterTest extends \PHPUnit_Framework_TestCase
         ];
     }
 
+    // This happens i.e. in React promises or Guzzle streams where stream wrappers are registered
+    // and no file or line are included in the trace because it's treated as internal function
     public function testExceptionTraceWithArgs()
     {
         if (defined('HHVM_VERSION')) {
             $this->markTestSkipped('Not supported in HHVM since it detects errors differently');
         }
 
-        // This happens i.e. in React promises or Guzzle streams where stream wrappers are registered
-        // and no file or line are included in the trace because it's treated as internal function
-        set_error_handler(function ($errno, $errstr, $errfile, $errline) {
-            throw new \ErrorException($errstr, 0, $errno, $errfile, $errline);
-        });
-
         try {
             // This will contain $resource and $wrappedResource as arguments in the trace item
             $resource = fopen('php://memory', 'rw+');
@@ -292,9 +288,12 @@ class NormalizerFormatterTest extends \PHPUnit_Framework_TestCase
             $wrappedResource = new TestFooNorm;
             $wrappedResource->foo = $resource;
             // Just do something stupid with a resource/wrapped resource as argument
-            array_keys($wrappedResource);
+            $arr = [$wrappedResource, null];
+            // modifying the array inside throws a "usort(): Array was modified by the user comparison function"
+            usort($arr, function ($a, $b) use (&$arr) {
+                $arr[] = 'new';
+            });
         } catch (\Throwable $e) {
-            restore_error_handler();
         }
 
         $formatter = new NormalizerFormatter();
diff --git a/tests/Monolog/Formatter/ScalarFormatterTest.php b/tests/Monolog/Formatter/ScalarFormatterTest.php
index 73707d9b..ea488e5d 100644
--- a/tests/Monolog/Formatter/ScalarFormatterTest.php
+++ b/tests/Monolog/Formatter/ScalarFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Formatter/WildfireFormatterTest.php b/tests/Monolog/Formatter/WildfireFormatterTest.php
index 0de8fd52..40ee82c0 100644
--- a/tests/Monolog/Formatter/WildfireFormatterTest.php
+++ b/tests/Monolog/Formatter/WildfireFormatterTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/AbstractHandlerTest.php b/tests/Monolog/Handler/AbstractHandlerTest.php
index 2cbcdcf0..b7451a73 100644
--- a/tests/Monolog/Handler/AbstractHandlerTest.php
+++ b/tests/Monolog/Handler/AbstractHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/AbstractProcessingHandlerTest.php b/tests/Monolog/Handler/AbstractProcessingHandlerTest.php
index 435e770c..58d09202 100644
--- a/tests/Monolog/Handler/AbstractProcessingHandlerTest.php
+++ b/tests/Monolog/Handler/AbstractProcessingHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/AmqpHandlerTest.php b/tests/Monolog/Handler/AmqpHandlerTest.php
index 9a41c394..c70e1621 100644
--- a/tests/Monolog/Handler/AmqpHandlerTest.php
+++ b/tests/Monolog/Handler/AmqpHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/BrowserConsoleHandlerTest.php b/tests/Monolog/Handler/BrowserConsoleHandlerTest.php
index 2ee66a8a..048ee1c9 100644
--- a/tests/Monolog/Handler/BrowserConsoleHandlerTest.php
+++ b/tests/Monolog/Handler/BrowserConsoleHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/BufferHandlerTest.php b/tests/Monolog/Handler/BufferHandlerTest.php
index 391c2374..f1338b40 100644
--- a/tests/Monolog/Handler/BufferHandlerTest.php
+++ b/tests/Monolog/Handler/BufferHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/ChromePHPHandlerTest.php b/tests/Monolog/Handler/ChromePHPHandlerTest.php
index ac5e7c44..c79818c5 100644
--- a/tests/Monolog/Handler/ChromePHPHandlerTest.php
+++ b/tests/Monolog/Handler/ChromePHPHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/CouchDBHandlerTest.php b/tests/Monolog/Handler/CouchDBHandlerTest.php
index b0d6ade7..f89a130b 100644
--- a/tests/Monolog/Handler/CouchDBHandlerTest.php
+++ b/tests/Monolog/Handler/CouchDBHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/DeduplicationHandlerTest.php b/tests/Monolog/Handler/DeduplicationHandlerTest.php
index 6b9fdfd1..491fd85c 100644
--- a/tests/Monolog/Handler/DeduplicationHandlerTest.php
+++ b/tests/Monolog/Handler/DeduplicationHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/DoctrineCouchDBHandlerTest.php b/tests/Monolog/Handler/DoctrineCouchDBHandlerTest.php
index 05f8bf76..f72f3237 100644
--- a/tests/Monolog/Handler/DoctrineCouchDBHandlerTest.php
+++ b/tests/Monolog/Handler/DoctrineCouchDBHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/DynamoDbHandlerTest.php b/tests/Monolog/Handler/DynamoDbHandlerTest.php
index cc99ad67..652dc962 100644
--- a/tests/Monolog/Handler/DynamoDbHandlerTest.php
+++ b/tests/Monolog/Handler/DynamoDbHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/ElasticSearchHandlerTest.php b/tests/Monolog/Handler/ElasticSearchHandlerTest.php
index 9ebf0623..c92a72b5 100644
--- a/tests/Monolog/Handler/ElasticSearchHandlerTest.php
+++ b/tests/Monolog/Handler/ElasticSearchHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/ErrorLogHandlerTest.php b/tests/Monolog/Handler/ErrorLogHandlerTest.php
index 66616ad8..d230fb1f 100644
--- a/tests/Monolog/Handler/ErrorLogHandlerTest.php
+++ b/tests/Monolog/Handler/ErrorLogHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/FilterHandlerTest.php b/tests/Monolog/Handler/FilterHandlerTest.php
index c45e3c14..0e64e769 100644
--- a/tests/Monolog/Handler/FilterHandlerTest.php
+++ b/tests/Monolog/Handler/FilterHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/FingersCrossedHandlerTest.php b/tests/Monolog/Handler/FingersCrossedHandlerTest.php
index 26fbec89..5b25a365 100644
--- a/tests/Monolog/Handler/FingersCrossedHandlerTest.php
+++ b/tests/Monolog/Handler/FingersCrossedHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -114,8 +114,8 @@ class FingersCrossedHandlerTest extends TestCase
     {
         $test = new TestHandler();
         $handler = new FingersCrossedHandler(function ($record, $handler) use ($test) {
-                    return $test;
-                });
+            return $test;
+        });
         $handler->handle($this->getRecord(Logger::DEBUG));
         $handler->handle($this->getRecord(Logger::INFO));
         $this->assertFalse($test->hasDebugRecords());
@@ -133,8 +133,8 @@ class FingersCrossedHandlerTest extends TestCase
     public function testHandleWithBadCallbackThrowsException()
     {
         $handler = new FingersCrossedHandler(function ($record, $handler) {
-                    return 'foo';
-                });
+            return 'foo';
+        });
         $handler->handle($this->getRecord(Logger::WARNING));
     }
 
diff --git a/tests/Monolog/Handler/FirePHPHandlerTest.php b/tests/Monolog/Handler/FirePHPHandlerTest.php
index bb30fdb4..b62e7fd0 100644
--- a/tests/Monolog/Handler/FirePHPHandlerTest.php
+++ b/tests/Monolog/Handler/FirePHPHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/FleepHookHandlerTest.php b/tests/Monolog/Handler/FleepHookHandlerTest.php
index 26946b13..11b5a654 100644
--- a/tests/Monolog/Handler/FleepHookHandlerTest.php
+++ b/tests/Monolog/Handler/FleepHookHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/FlowdockHandlerTest.php b/tests/Monolog/Handler/FlowdockHandlerTest.php
index 4d8d0a4f..8df847ab 100644
--- a/tests/Monolog/Handler/FlowdockHandlerTest.php
+++ b/tests/Monolog/Handler/FlowdockHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/GelfHandlerLegacyTest.php b/tests/Monolog/Handler/GelfHandlerLegacyTest.php
index 02a234dc..00150a13 100644
--- a/tests/Monolog/Handler/GelfHandlerLegacyTest.php
+++ b/tests/Monolog/Handler/GelfHandlerLegacyTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/GelfHandlerTest.php b/tests/Monolog/Handler/GelfHandlerTest.php
index e1b4f7aa..bc06fa32 100644
--- a/tests/Monolog/Handler/GelfHandlerTest.php
+++ b/tests/Monolog/Handler/GelfHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/GelfMockMessagePublisher.php b/tests/Monolog/Handler/GelfMockMessagePublisher.php
index 873d92fb..b1e94ed3 100644
--- a/tests/Monolog/Handler/GelfMockMessagePublisher.php
+++ b/tests/Monolog/Handler/GelfMockMessagePublisher.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/GroupHandlerTest.php b/tests/Monolog/Handler/GroupHandlerTest.php
index 4d7c65cc..0e3b9bb5 100644
--- a/tests/Monolog/Handler/GroupHandlerTest.php
+++ b/tests/Monolog/Handler/GroupHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/HandlerWrapperTest.php b/tests/Monolog/Handler/HandlerWrapperTest.php
index b27c0093..4a347412 100644
--- a/tests/Monolog/Handler/HandlerWrapperTest.php
+++ b/tests/Monolog/Handler/HandlerWrapperTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/HipChatHandlerTest.php b/tests/Monolog/Handler/HipChatHandlerTest.php
index d95e188b..0d2e8c0c 100644
--- a/tests/Monolog/Handler/HipChatHandlerTest.php
+++ b/tests/Monolog/Handler/HipChatHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/LogEntriesHandlerTest.php b/tests/Monolog/Handler/LogEntriesHandlerTest.php
index a917e519..b6d2924b 100644
--- a/tests/Monolog/Handler/LogEntriesHandlerTest.php
+++ b/tests/Monolog/Handler/LogEntriesHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/MailHandlerTest.php b/tests/Monolog/Handler/MailHandlerTest.php
index c489e263..ee686adc 100644
--- a/tests/Monolog/Handler/MailHandlerTest.php
+++ b/tests/Monolog/Handler/MailHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -25,7 +25,7 @@ class MailHandlerTest extends TestCase
         $formatter->expects($this->once())
             ->method('formatBatch'); // Each record is formatted
 
-        $handler = $this->getMockForAbstractClass('Monolog\\Handler\\MailHandler');
+        $handler = $this->getMockForAbstractClass('Monolog\\Handler\\MailHandler', [], '', true, true, true, ['send', 'write']);
         $handler->expects($this->once())
             ->method('send');
         $handler->expects($this->never())
diff --git a/tests/Monolog/Handler/MockRavenClient.php b/tests/Monolog/Handler/MockRavenClient.php
index a0833225..d344d342 100644
--- a/tests/Monolog/Handler/MockRavenClient.php
+++ b/tests/Monolog/Handler/MockRavenClient.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/MongoDBHandlerTest.php b/tests/Monolog/Handler/MongoDBHandlerTest.php
index 0cddea3d..7333ef62 100644
--- a/tests/Monolog/Handler/MongoDBHandlerTest.php
+++ b/tests/Monolog/Handler/MongoDBHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/NativeMailerHandlerTest.php b/tests/Monolog/Handler/NativeMailerHandlerTest.php
index 9ac08be6..d4aef95e 100644
--- a/tests/Monolog/Handler/NativeMailerHandlerTest.php
+++ b/tests/Monolog/Handler/NativeMailerHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/NewRelicHandlerTest.php b/tests/Monolog/Handler/NewRelicHandlerTest.php
index 7471003b..a71bbf88 100644
--- a/tests/Monolog/Handler/NewRelicHandlerTest.php
+++ b/tests/Monolog/Handler/NewRelicHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/NullHandlerTest.php b/tests/Monolog/Handler/NullHandlerTest.php
index 89c6639e..b7e482ba 100644
--- a/tests/Monolog/Handler/NullHandlerTest.php
+++ b/tests/Monolog/Handler/NullHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/PHPConsoleHandlerTest.php b/tests/Monolog/Handler/PHPConsoleHandlerTest.php
index ffdb0c6a..0836b995 100644
--- a/tests/Monolog/Handler/PHPConsoleHandlerTest.php
+++ b/tests/Monolog/Handler/PHPConsoleHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/ProcessHandlerTest.php b/tests/Monolog/Handler/ProcessHandlerTest.php
index 9b739e1f..011c7c59 100644
--- a/tests/Monolog/Handler/ProcessHandlerTest.php
+++ b/tests/Monolog/Handler/ProcessHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/PsrHandlerTest.php b/tests/Monolog/Handler/PsrHandlerTest.php
index 7a04bb3f..63988090 100644
--- a/tests/Monolog/Handler/PsrHandlerTest.php
+++ b/tests/Monolog/Handler/PsrHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/PushoverHandlerTest.php b/tests/Monolog/Handler/PushoverHandlerTest.php
index b4ca524c..e5336ab0 100644
--- a/tests/Monolog/Handler/PushoverHandlerTest.php
+++ b/tests/Monolog/Handler/PushoverHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/RavenHandlerTest.php b/tests/Monolog/Handler/RavenHandlerTest.php
index ca3e8ac7..d4325e5a 100644
--- a/tests/Monolog/Handler/RavenHandlerTest.php
+++ b/tests/Monolog/Handler/RavenHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -189,7 +189,7 @@ class RavenHandlerTest extends TestCase
             $this->getRecord(Logger::INFO, 'information'),
         ];
 
-        $handler = $this->getMock('Monolog\Handler\RavenHandler', null, [$this->getRavenClient()]);
+        $handler = $this->getMock('Monolog\Handler\RavenHandler', ['handle'], [$this->getRavenClient()]);
         $handler->expects($this->never())->method('handle');
         $handler->setLevel(Logger::ERROR);
         $handler->handleBatch($records);
diff --git a/tests/Monolog/Handler/RedisHandlerTest.php b/tests/Monolog/Handler/RedisHandlerTest.php
index 57bfb34c..8363c9a2 100644
--- a/tests/Monolog/Handler/RedisHandlerTest.php
+++ b/tests/Monolog/Handler/RedisHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/RotatingFileHandlerTest.php b/tests/Monolog/Handler/RotatingFileHandlerTest.php
index 3f91f179..13b8a4c6 100644
--- a/tests/Monolog/Handler/RotatingFileHandlerTest.php
+++ b/tests/Monolog/Handler/RotatingFileHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -111,10 +111,10 @@ class RotatingFileHandlerTest extends TestCase
             return $now + 86400 * $ago;
         };
         $monthCallback = function ($ago) {
-            return gmmktime(0, 0, 0, date('n') + $ago, date('d'), date('Y'));
+            return gmmktime(0, 0, 0, (int) (date('n') + $ago), (int) date('d'), (int) date('Y'));
         };
         $yearCallback = function ($ago) {
-            return gmmktime(0, 0, 0, date('n'), date('d'), date('Y') + $ago);
+            return gmmktime(0, 0, 0, (int) date('n'), (int) date('d'), (int) (date('Y') + $ago));
         };
 
         return [
diff --git a/tests/Monolog/Handler/SamplingHandlerTest.php b/tests/Monolog/Handler/SamplingHandlerTest.php
index 55637c60..90f5c9b3 100644
--- a/tests/Monolog/Handler/SamplingHandlerTest.php
+++ b/tests/Monolog/Handler/SamplingHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/SlackHandlerTest.php b/tests/Monolog/Handler/SlackHandlerTest.php
index 3cbb7e4f..d42c19b0 100644
--- a/tests/Monolog/Handler/SlackHandlerTest.php
+++ b/tests/Monolog/Handler/SlackHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/SocketHandlerTest.php b/tests/Monolog/Handler/SocketHandlerTest.php
index 5aaead64..4574859e 100644
--- a/tests/Monolog/Handler/SocketHandlerTest.php
+++ b/tests/Monolog/Handler/SocketHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/StreamHandlerTest.php b/tests/Monolog/Handler/StreamHandlerTest.php
index b0d7d7fa..377e2964 100644
--- a/tests/Monolog/Handler/StreamHandlerTest.php
+++ b/tests/Monolog/Handler/StreamHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/SwiftMailerHandlerTest.php b/tests/Monolog/Handler/SwiftMailerHandlerTest.php
index 64ad0887..ec7fc217 100644
--- a/tests/Monolog/Handler/SwiftMailerHandlerTest.php
+++ b/tests/Monolog/Handler/SwiftMailerHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/SyslogHandlerTest.php b/tests/Monolog/Handler/SyslogHandlerTest.php
index 8f9e46bf..dd31f532 100644
--- a/tests/Monolog/Handler/SyslogHandlerTest.php
+++ b/tests/Monolog/Handler/SyslogHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/SyslogUdpHandlerTest.php b/tests/Monolog/Handler/SyslogUdpHandlerTest.php
index df3b16b2..25d7c58e 100644
--- a/tests/Monolog/Handler/SyslogUdpHandlerTest.php
+++ b/tests/Monolog/Handler/SyslogUdpHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/TestHandlerTest.php b/tests/Monolog/Handler/TestHandlerTest.php
index 9b12d361..4fa20bb1 100644
--- a/tests/Monolog/Handler/TestHandlerTest.php
+++ b/tests/Monolog/Handler/TestHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/UdpSocketTest.php b/tests/Monolog/Handler/UdpSocketTest.php
index 200857a1..de0f7fb8 100644
--- a/tests/Monolog/Handler/UdpSocketTest.php
+++ b/tests/Monolog/Handler/UdpSocketTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/WhatFailureGroupHandlerTest.php b/tests/Monolog/Handler/WhatFailureGroupHandlerTest.php
index d763ecbd..60f51755 100644
--- a/tests/Monolog/Handler/WhatFailureGroupHandlerTest.php
+++ b/tests/Monolog/Handler/WhatFailureGroupHandlerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Handler/ZendMonitorHandlerTest.php b/tests/Monolog/Handler/ZendMonitorHandlerTest.php
index 999ad1d3..4879ebef 100644
--- a/tests/Monolog/Handler/ZendMonitorHandlerTest.php
+++ b/tests/Monolog/Handler/ZendMonitorHandlerTest.php
@@ -1,4 +1,5 @@
-<?php
+<?php declare(strict_types=1);
+
 /*
  * This file is part of the Monolog package.
  *
diff --git a/tests/Monolog/LoggerTest.php b/tests/Monolog/LoggerTest.php
index 005eeb25..75c2dbd3 100644
--- a/tests/Monolog/LoggerTest.php
+++ b/tests/Monolog/LoggerTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
@@ -487,7 +487,9 @@ class LoggerTest extends \PHPUnit_Framework_TestCase
     public function setTimezoneProvider()
     {
         return array_map(
-            function ($tz) { return [new \DateTimeZone($tz)]; },
+            function ($tz) {
+                return [new \DateTimeZone($tz)];
+            },
             \DateTimeZone::listIdentifiers()
         );
     }
diff --git a/tests/Monolog/Processor/GitProcessorTest.php b/tests/Monolog/Processor/GitProcessorTest.php
index 2dc9ae79..0059e6d3 100644
--- a/tests/Monolog/Processor/GitProcessorTest.php
+++ b/tests/Monolog/Processor/GitProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/IntrospectionProcessorTest.php b/tests/Monolog/Processor/IntrospectionProcessorTest.php
index 38793efe..5f5d9aea 100644
--- a/tests/Monolog/Processor/IntrospectionProcessorTest.php
+++ b/tests/Monolog/Processor/IntrospectionProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/MemoryPeakUsageProcessorTest.php b/tests/Monolog/Processor/MemoryPeakUsageProcessorTest.php
index 1893e66d..cd805276 100644
--- a/tests/Monolog/Processor/MemoryPeakUsageProcessorTest.php
+++ b/tests/Monolog/Processor/MemoryPeakUsageProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/MemoryUsageProcessorTest.php b/tests/Monolog/Processor/MemoryUsageProcessorTest.php
index 8229a482..a4809cbe 100644
--- a/tests/Monolog/Processor/MemoryUsageProcessorTest.php
+++ b/tests/Monolog/Processor/MemoryUsageProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/ProcessIdProcessorTest.php b/tests/Monolog/Processor/ProcessIdProcessorTest.php
index f20ce9e9..ec39e8ee 100644
--- a/tests/Monolog/Processor/ProcessIdProcessorTest.php
+++ b/tests/Monolog/Processor/ProcessIdProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/PsrLogMessageProcessorTest.php b/tests/Monolog/Processor/PsrLogMessageProcessorTest.php
index af366377..77db8425 100644
--- a/tests/Monolog/Processor/PsrLogMessageProcessorTest.php
+++ b/tests/Monolog/Processor/PsrLogMessageProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/TagProcessorTest.php b/tests/Monolog/Processor/TagProcessorTest.php
index ec514d77..da84378b 100644
--- a/tests/Monolog/Processor/TagProcessorTest.php
+++ b/tests/Monolog/Processor/TagProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/UidProcessorTest.php b/tests/Monolog/Processor/UidProcessorTest.php
index 7cb63654..927d5648 100644
--- a/tests/Monolog/Processor/UidProcessorTest.php
+++ b/tests/Monolog/Processor/UidProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/Processor/WebProcessorTest.php b/tests/Monolog/Processor/WebProcessorTest.php
index abaa1aee..6da6ab89 100644
--- a/tests/Monolog/Processor/WebProcessorTest.php
+++ b/tests/Monolog/Processor/WebProcessorTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/PsrLogCompatTest.php b/tests/Monolog/PsrLogCompatTest.php
index ab899449..a4bbcd0c 100644
--- a/tests/Monolog/PsrLogCompatTest.php
+++ b/tests/Monolog/PsrLogCompatTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/Monolog/RegistryTest.php b/tests/Monolog/RegistryTest.php
index f1d1abac..ef4e452e 100644
--- a/tests/Monolog/RegistryTest.php
+++ b/tests/Monolog/RegistryTest.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index ab5efb79..d475dd33 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 /*
  * This file is part of the Monolog package.