diff --git a/src/Symfony/Bridge/Twig/Extension/FormExtension.php b/src/Symfony/Bridge/Twig/Extension/FormExtension.php
index 6e6274dcc4..beed1c95b3 100644
--- a/src/Symfony/Bridge/Twig/Extension/FormExtension.php
+++ b/src/Symfony/Bridge/Twig/Extension/FormExtension.php
@@ -106,7 +106,7 @@ class FormExtension extends AbstractExtension implements InitRuntimeInterface
     {
         return array(
             new TwigTest('selectedchoice', 'Symfony\Bridge\Twig\Extension\twig_is_selected_choice'),
-            new TwigTest('rootform', array($this, 'isRootForm')),
+            new TwigTest('rootform', 'Symfony\Bridge\Twig\Extension\twig_is_root_form'),
         );
     }
 
@@ -166,14 +166,6 @@ class FormExtension extends AbstractExtension implements InitRuntimeInterface
         unset($this->$name);
     }
 
-    /**
-     * @internal
-     */
-    public function isRootForm(FormView $formView)
-    {
-        return null === $formView->parent;
-    }
-
     /**
      * {@inheritdoc}
      */
@@ -202,3 +194,11 @@ function twig_is_selected_choice(ChoiceView $choice, $selectedValue)
 
     return $choice->value === $selectedValue;
 }
+
+/**
+ * @internal
+ */
+function twig_is_root_form(FormView $formView)
+{
+    return null === $formView->parent;
+}