diff --git a/src/Symfony/Component/HttpFoundation/HeaderUtils.php b/src/Symfony/Component/HttpFoundation/HeaderUtils.php
index 6421b1121c..9886850905 100644
--- a/src/Symfony/Component/HttpFoundation/HeaderUtils.php
+++ b/src/Symfony/Component/HttpFoundation/HeaderUtils.php
@@ -228,7 +228,7 @@ class HeaderUtils
             if (false === $i = strpos($k, '[')) {
                 $q[] = bin2hex($k).$v;
             } else {
-                $q[] = substr_replace($k, bin2hex(substr($k, 0, $i)), 0, $i).$v;
+                $q[] = bin2hex(substr($k, 0, $i)).rawurlencode(substr($k, $i)).$v;
             }
         }
 
diff --git a/src/Symfony/Component/HttpFoundation/Tests/HeaderUtilsTest.php b/src/Symfony/Component/HttpFoundation/Tests/HeaderUtilsTest.php
index b8ad4dfd0a..6d7df8b3b3 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/HeaderUtilsTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/HeaderUtilsTest.php
@@ -151,6 +151,7 @@ class HeaderUtilsTest extends TestCase
             ['a[b]=c', 'a%5Bb%5D=c'],
             ['a[b][c.d]=c', 'a%5Bb%5D%5Bc.d%5D=c'],
             ['a%5Bb%5D=c'],
+            ['f[%2525][%26][%3D][p.c]=d', 'f%5B%2525%5D%5B%26%5D%5B%3D%5D%5Bp.c%5D=d'],
         ];
     }