diff --git a/src/Forms/DataObjectVersionFormFactory.php b/src/Forms/DataObjectVersionFormFactory.php
index 0790335..26f9fdb 100644
--- a/src/Forms/DataObjectVersionFormFactory.php
+++ b/src/Forms/DataObjectVersionFormFactory.php
@@ -91,7 +91,7 @@ public function isReadonlyFormType(array $context)
         return in_array($this->getFormType($context), $this->config()->get('readonly_types') ?? []);
     }
 
-    protected function getFormFields(?RequestHandler $controller = null, $name, $context = [])
+    protected function getFormFields(?RequestHandler $controller, $name, $context = [])
     {
         $record = $context['Record'];
         /** @var FieldList $fields */