diff --git a/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php b/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
index 6637ac8c63..915c43fa62 100644
--- a/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
+++ b/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
@@ -22,6 +22,8 @@ class DependencyInjectionExtension implements FormExtensionInterface
 
     private $typeServiceIds;
 
+    private $typeExtensionServiceIds;
+
     private $guesserServiceIds;
 
     private $guesser;