diff --git a/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php b/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php
index 12194a3..36a077c 100644
--- a/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php
+++ b/core/lib/Drupal/Core/Entity/Entity/EntityFormDisplay.php
@@ -232,6 +232,7 @@ public function __sleep() {
     // Only store the definition, not external objects or derived data.
     $keys = array_keys($this->toArray());
     $keys[] = 'entityTypeId';
+    $keys[] = 'enforceIsNew';
     return $keys;
   }
 
@@ -241,7 +242,9 @@ public function __sleep() {
   public function __wakeup() {
     // Run the values from self::toArray() through __construct().
     $values = array_intersect_key($this->toArray(), get_object_vars($this));
+    $is_new = $this->isNew();
     $this->__construct($values, $this->entityTypeId);
+    $this->enforceIsNew($is_new);
   }
 
   /**
diff --git a/core/modules/field_ui/src/Form/EntityDisplayFormBase.php b/core/modules/field_ui/src/Form/EntityDisplayFormBase.php
index 5a936ab..b5d370d 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayFormBase.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayFormBase.php
@@ -569,19 +569,6 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function save(array $form, FormStateInterface $form_state) {
-    // Work around the fact that entity display are never guaranteed to be
-    // present, not even the 'default' one.
-    if (!$this->entityManager->getStorage($this->entity->getEntityTypeId())->load($this->entity->id())) {
-      $this->entity->enforceIsNew();
-    }
-
-    parent::save($form, $form_state);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
     $form_values = $form_state->getValues();
 
diff --git a/core/modules/field_ui/src/Tests/FieldUIRouteTest.php b/core/modules/field_ui/src/Tests/FieldUIRouteTest.php
index b97bc83..ac7d01f 100644
--- a/core/modules/field_ui/src/Tests/FieldUIRouteTest.php
+++ b/core/modules/field_ui/src/Tests/FieldUIRouteTest.php
@@ -65,6 +65,7 @@ public function testFieldUIRoutes() {
 
     $edit = array('display_modes_custom[register]' => TRUE);
     $this->drupalPostForm(NULL, $edit, t('Save'));
+    $this->assertResponse(200);
     $this->drupalGet('admin/config/people/accounts/form-display/register');
     $this->assertTitle('Manage form display | Drupal');
     $this->assertLocalTasks();