diff --git a/Form/Extension/DescriptionFormTypeExtension.php b/Form/Extension/DescriptionFormTypeExtension.php
index 151d803..1a3e815 100644
--- a/Form/Extension/DescriptionFormTypeExtension.php
+++ b/Form/Extension/DescriptionFormTypeExtension.php
@@ -60,7 +60,7 @@ class DescriptionFormTypeExtension extends AbstractTypeExtension
     /**
      * {@inheritdoc}
      */
-    public static function getExtendedTypes()
+    public static function getExtendedTypes(): iterable
     {
         return [LegacyFormHelper::getType('Symfony\Component\Form\Extension\Core\Type\FormType')];
     }