diff --git a/src/Symfony/Component/HttpKernel/HttpCache/Esi.php b/src/Symfony/Component/HttpKernel/HttpCache/Esi.php
index 3ac0e49587..2c48163c17 100644
--- a/src/Symfony/Component/HttpKernel/HttpCache/Esi.php
+++ b/src/Symfony/Component/HttpKernel/HttpCache/Esi.php
@@ -64,7 +64,7 @@ class Esi
             return false;
         }
 
-        return (Boolean) preg_match('#ESI/1.0#', $value);
+        return false !== strpos($value, 'ESI/1.0');
     }
 
     /**