diff --git a/src/Monolog/Processor/WebProcessor.php b/src/Monolog/Processor/WebProcessor.php
index 4c2bc191..7021dcf7 100644
--- a/src/Monolog/Processor/WebProcessor.php
+++ b/src/Monolog/Processor/WebProcessor.php
@@ -18,12 +18,27 @@ namespace Monolog\Processor;
  */
 class WebProcessor
 {
+    /**
+     * @var array|\ArrayAccess
+     */
     protected $serverData;
 
     /**
-     * @param mixed $serverData array or object w/ ArrayAccess that provides access to the $_SERVER data
+     * @var array
      */
-    public function __construct($serverData = null)
+    protected $extraFields = array(
+        'url'         => 'REQUEST_URI',
+        'ip'          => 'REMOTE_ADDR',
+        'http_method' => 'REQUEST_METHOD',
+        'server'      => 'SERVER_NAME',
+        'referrer'    => 'HTTP_REFERER',
+    );
+
+    /**
+     * @param mixed      $serverData  Array or object w/ ArrayAccess that provides access to the $_SERVER data
+     * @param array|null $extraFields Extra field names to be added (all available by default)
+     */
+    public function __construct($serverData = null, array $extraFields = null)
     {
         if (null === $serverData) {
             $this->serverData =& $_SERVER;
@@ -32,6 +47,14 @@ class WebProcessor
         } else {
             throw new \UnexpectedValueException('$serverData must be an array or object implementing ArrayAccess.');
         }
+
+        if (null !== $extraFields) {
+            foreach (array_keys($this->extraFields) as $fieldName) {
+                if (!in_array($fieldName, $extraFields)) {
+                    unset($this->extraFields[$fieldName]);
+                }
+            }
+        }
     }
 
     /**
@@ -46,21 +69,25 @@ class WebProcessor
             return $record;
         }
 
-        $record['extra'] = array_merge(
-            $record['extra'],
-            array(
-                'url'         => $this->serverData['REQUEST_URI'],
-                'ip'          => isset($this->serverData['REMOTE_ADDR']) ? $this->serverData['REMOTE_ADDR'] : null,
-                'http_method' => isset($this->serverData['REQUEST_METHOD']) ? $this->serverData['REQUEST_METHOD'] : null,
-                'server'      => isset($this->serverData['SERVER_NAME']) ? $this->serverData['SERVER_NAME'] : null,
-                'referrer'    => isset($this->serverData['HTTP_REFERER']) ? $this->serverData['HTTP_REFERER'] : null,
-            )
-        );
-
-        if (isset($this->serverData['UNIQUE_ID'])) {
-            $record['extra']['unique_id'] = $this->serverData['UNIQUE_ID'];
-        }
+        $record['extra'] = $this->appendExtraFields($record['extra']);
 
         return $record;
     }
+
+    /**
+     * @param  array $extra
+     * @return array
+     */
+    private function appendExtraFields(array $extra)
+    {
+        foreach ($this->extraFields as $extraName => $serverName) {
+            $extra[$extraName] = isset($this->serverData[$serverName]) ? $this->serverData[$serverName] : null;
+        }
+
+        if (isset($this->serverData['UNIQUE_ID'])) {
+            $extra['unique_id'] = $this->serverData['UNIQUE_ID'];
+        }
+
+        return $extra;
+    }
 }
diff --git a/tests/Monolog/Processor/WebProcessorTest.php b/tests/Monolog/Processor/WebProcessorTest.php
index df29fdd6..dba89412 100644
--- a/tests/Monolog/Processor/WebProcessorTest.php
+++ b/tests/Monolog/Processor/WebProcessorTest.php
@@ -73,6 +73,21 @@ class WebProcessorTest extends TestCase
         $this->assertFalse(isset($record['extra']['unique_id']));
     }
 
+    public function testProcessorAddsOnlyRequestedExtraFields()
+    {
+        $server = array(
+            'REQUEST_URI'    => 'A',
+            'REMOTE_ADDR'    => 'B',
+            'REQUEST_METHOD' => 'C',
+            'SERVER_NAME'    => 'F',
+        );
+
+        $processor = new WebProcessor($server, array('url', 'http_method'));
+        $record = $processor($this->getRecord());
+
+        $this->assertSame(array('url' => 'A', 'http_method' => 'C'), $record['extra']);
+    }
+
     /**
      * @expectedException UnexpectedValueException
      */