diff --git a/src/Symfony/Component/HttpFoundation/Request.php b/src/Symfony/Component/HttpFoundation/Request.php
index 3bbcb4ce72..12a083f41c 100644
--- a/src/Symfony/Component/HttpFoundation/Request.php
+++ b/src/Symfony/Component/HttpFoundation/Request.php
@@ -1847,7 +1847,7 @@ class Request
 
         $len = strlen($prefix);
 
-        if (preg_match("#^(%[[:xdigit:]]{2}|.){{$len}}#", $string, $match)) {
+        if (preg_match(sprintf('#^(%%[[:xdigit:]]{2}|.){%d}#', $len), $string, $match)) {
             return $match[0];
         }