diff --git a/core/modules/content_translation/content_translation.module b/core/modules/content_translation/content_translation.module
index 10f6a92..c1ea11a 100644
--- a/core/modules/content_translation/content_translation.module
+++ b/core/modules/content_translation/content_translation.module
@@ -338,16 +338,18 @@ function _content_translation_menu_strip_loaders($path) {
  * Implements hook_entity_prepare_form().
  */
 function content_translation_entity_prepare_form(EntityInterface $entity, $form_display, $operation, array &$form_state) {
-  $languages = language_list();
-  $source = Drupal::request()->get('content_translation_source');
-  $target = Drupal::request()->get('content_translation_target');
-  content_translation_prepare_translation_form($entity, isset($languages[$source]) ? $source : FALSE, isset($languages[$target]) ? $target : NULL, $form_state);
+  if ($entity instanceof ContentEntityInterface) {
+    $languages = language_list();
+    $source = Drupal::request()->get('content_translation_source');
+    $target = Drupal::request()->get('content_translation_target');
+    content_translation_prepare_translation_form($entity, isset($languages[$source]) ? $source : FALSE, isset($languages[$target]) ? $target : NULL, $form_state);
+  }
 }
 
 /**
  * Prepares the entity and the form state to display a translation form.
  *
- * @param EntityInterface $entity
+ * @param ContentEntityInterface $entity
  *   The entity being translated.
  * @param string $source
  *   The language code to be used as source.
@@ -356,7 +358,7 @@ function content_translation_entity_prepare_form(EntityInterface $entity, $form_
  * @param array $form_state
  *   An associative array representing the state of the form.
  */
-function content_translation_prepare_translation_form(EntityInterface $entity, $source, $target, array &$form_state) {
+function content_translation_prepare_translation_form(ContentEntityInterface $entity, $source, $target, array &$form_state) {
   if (empty($form_state['content_translation']['prepared']) && $entity->isTranslatable() && content_translation_access($entity, $source ? 'create' : 'update')) {
     // Avoid preparing the entity form twice.
     $form_state['content_translation']['prepared'] = TRUE;