diff --git a/src/Symfony/Component/HttpFoundation/ServerBag.php b/src/Symfony/Component/HttpFoundation/ServerBag.php
index fcb41cc5ee..ed807f2eb6 100644
--- a/src/Symfony/Component/HttpFoundation/ServerBag.php
+++ b/src/Symfony/Component/HttpFoundation/ServerBag.php
@@ -28,12 +28,13 @@ class ServerBag extends ParameterBag
     public function getHeaders()
     {
         $headers = array();
+        $contentHeaders = array('CONTENT_LENGTH' => true, 'CONTENT_MD5' => true, 'CONTENT_TYPE' => true);
         foreach ($this->parameters as $key => $value) {
-            if (0 === strpos($key, 'HTTP_')) {
+            if ('HTTP_' === substr($key, 0, 5)) {
                 $headers[substr($key, 5)] = $value;
             }
             // CONTENT_* are not prefixed with HTTP_
-            elseif (in_array($key, array('CONTENT_LENGTH', 'CONTENT_MD5', 'CONTENT_TYPE'))) {
+            elseif (isset($contentHeaders[$key])) {
                 $headers[$key] = $value;
             }
         }