diff --git a/src/Symfony/Component/Cache/Traits/MemcachedTrait.php b/src/Symfony/Component/Cache/Traits/MemcachedTrait.php
index 9b7a84ab59..999687de99 100644
--- a/src/Symfony/Component/Cache/Traits/MemcachedTrait.php
+++ b/src/Symfony/Component/Cache/Traits/MemcachedTrait.php
@@ -26,7 +26,7 @@ trait MemcachedTrait
         'persistent_id' => null,
         'username' => null,
         'password' => null,
-        'serializer' => 'php',
+        \Memcached::OPT_SERIALIZER => \Memcached::SERIALIZER_PHP,
     ];
 
     private $client;