diff --git a/core/modules/entity/lib/Drupal/entity/EntityFormController.php b/core/modules/entity/lib/Drupal/entity/EntityFormController.php
index 2061ed5..5634888 100644
--- a/core/modules/entity/lib/Drupal/entity/EntityFormController.php
+++ b/core/modules/entity/lib/Drupal/entity/EntityFormController.php
@@ -282,6 +282,8 @@ class EntityFormController implements EntityFormControllerInterface {
    *   The current form state.
    */
   protected function setFormInstance(&$form_state) {
+    // @todo Remove this. We need to find a way not to hard-code the controller
+    // form state key to enable multiple-entity forms in a single form.
     $this->form_state = &$form_state;
     $form_state['controller'] = $this;
   }