diff --git a/cookbook/form/dynamic_form_modification.rst b/cookbook/form/dynamic_form_modification.rst
index 92d7521f4e4..6124d9b6f24 100644
--- a/cookbook/form/dynamic_form_modification.rst
+++ b/cookbook/form/dynamic_form_modification.rst
@@ -721,10 +721,11 @@ all of this, use a listener::
 
     use Symfony\Component\Form\FormBuilderInterface;
     use Symfony\Component\Form\FormEvents;
+    use Symfony\Component\Form\FormEvent;
 
     public function buildForm(FormBuilderInterface $builder, array $options)
     {
-        $builder->addEventListener(FormEvents::POST_SUBMIT, function ($event) {
+        $builder->addEventListener(FormEvents::POST_SUBMIT, function (FormEvent $event) {
             $event->stopPropagation();
         }, 900); // Always set a higher priority than ValidationListener