diff --git a/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php b/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php
index 2e5c872..e9aaab2 100644
--- a/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php
+++ b/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php
@@ -94,18 +94,7 @@ protected function getFormObject(Request $request, $form_arg, $_values = FALSE)
           $defaults_class = new $class();
         }
 
-        // Using reflection, find all of the parameters needed by the form in
-        // the request attributes.
-        $attributes = $request->attributes->all();
-        $reflection = new \ReflectionMethod($class, $method);
-        $params = $reflection->getParameters();
-        $args = array();
-        foreach ($params as $param) {
-          if (array_key_exists($param->name, $attributes)) {
-            $args[] = $attributes[$param->name];
-          }
-        }
-        $values = call_user_func_array(array($defaults_class, $method), $args);
+        $values = call_user_func(array($defaults_class, $method), $request);
       }
 
       $entity = $manager->getStorageController($entity_type)->create($values);
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/Controller/CustomBlockController.php b/core/modules/block/custom_block/lib/Drupal/custom_block/Controller/CustomBlockController.php
index 1b4345a..dcc241c 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/Controller/CustomBlockController.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Controller/CustomBlockController.php
@@ -82,7 +82,7 @@ public function add() {
   /**
    * Presents the custom block creation form.
    *
-   * @param Drupal\custom_block\Plugin\Core\Entity\CustomBlockType $custom_block_type
+   * @param \Drupal\custom_block\Plugin\Core\Entity\CustomBlockType $custom_block_type
    *   The custom block type to add.
    *
    * @return array
@@ -106,13 +106,14 @@ protected function addForm(CustomBlockType $custom_block_type) {
   /**
    * Returns default values for the new entity.
    *
-   * @param Drupal\custom_block\Plugin\Core\Entity\CustomBlockType $custom_block_type
-   *   The custom block type to add.
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
    *
    * @return array
    *   Array of default values to use whilst creating entity form.
    */
-  public function defaults(CustomBlockType $custom_block_type) {
+  public function defaults(Request $request) {
+    $custom_block_type = $request->attributes->get('custom_block_type');
     return array(
       'type' => $custom_block_type->id()
     );