diff --git a/src/Monolog/Handler/BufferHandler.php b/src/Monolog/Handler/BufferHandler.php
index 7b5ebbbe..c799b6b9 100644
--- a/src/Monolog/Handler/BufferHandler.php
+++ b/src/Monolog/Handler/BufferHandler.php
@@ -163,7 +163,7 @@ class BufferHandler extends AbstractHandler implements ProcessableHandlerInterfa
         throw new \UnexpectedValueException('The nested handler of type '.\get_class($this->handler).' does not support formatters.');
     }
 
-    public function setHandler(HandlerInterface $handler)
+    public function setHandler(HandlerInterface $handler): void
     {
         $this->handler = $handler;
     }
diff --git a/tests/Monolog/Formatter/ElasticsearchFormatterTest.php b/tests/Monolog/Formatter/ElasticsearchFormatterTest.php
index 438bbfd3..1a53c66e 100644
--- a/tests/Monolog/Formatter/ElasticsearchFormatterTest.php
+++ b/tests/Monolog/Formatter/ElasticsearchFormatterTest.php
@@ -34,7 +34,7 @@ class ElasticsearchFormatterTest extends TestCase
 
         // Expected values
         $expected = $msg->toArray();
-        $expected['datetime'] = '1970-01-01T00:00:00+0000';
+        $expected['datetime'] = '1970-01-01T00:00:00+00:00';
         $expected['context'] = [
             'class' => ['stdClass' => []],
             'foo' => 7,