diff --git a/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php b/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php
index 0d68e77..94e115f 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php
@@ -38,6 +38,17 @@ public function getFormId() {
   /**
    * {@inheritdoc}
    */
+  public function buildForm(array $form, array &$form_state, $entity_type = NULL, $bundle = NULL) {
+    if ($this->getRequest()->attributes->has('view_mode_name')) {
+      $this->mode = $this->getRequest()->attributes->get('view_mode_name');
+    }
+
+    parent::buildForm($form, $form_state, $entity_type, $bundle);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   protected function buildFieldRow($field_id, FieldInstanceInterface $instance, EntityDisplayBaseInterface $entity_display, array $form, array &$form_state) {
     $field_row = parent::buildFieldRow($field_id, $instance, $entity_display, $form, $form_state);
     $display_options = $entity_display->getComponent($field_id);
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverviewBase.php b/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverviewBase.php
index 9834005..06a4bdc 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverviewBase.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverviewBase.php
@@ -82,17 +82,10 @@ public function getRegions() {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, array &$form_state, $entity_type = NULL, $bundle = NULL, $mode = NULL) {
+  public function buildForm(array $form, array &$form_state, $entity_type = NULL, $bundle = NULL) {
     parent::buildForm($form, $form_state, $entity_type, $bundle);
 
-    $raw_variables = $this->getRequest()->attributes->get('_raw_variables')->all();
-    if (isset($raw_variables['form_mode_name'])) {
-      $this->mode = $raw_variables['form_mode_name'];
-    }
-    elseif (isset($raw_variables['view_mode_name'])) {
-      $this->mode = $raw_variables['view_mode_name'];
-    }
-    else {
+    if (empty($this->mode)) {
       $this->mode = 'default';
     }
 
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/FormDisplayOverview.php b/core/modules/field_ui/lib/Drupal/field_ui/FormDisplayOverview.php
index a1e8d8b..19cf261 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/FormDisplayOverview.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/FormDisplayOverview.php
@@ -38,6 +38,17 @@ public function getFormId() {
   /**
    * {@inheritdoc}
    */
+  public function buildForm(array $form, array &$form_state, $entity_type = NULL, $bundle = NULL) {
+    if ($this->getRequest()->attributes->has('form_mode_name')) {
+      $this->mode = $this->getRequest()->attributes->get('form_mode_name');
+    }
+
+    parent::buildForm($form, $form_state, $entity_type, $bundle);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   protected function buildFieldRow($field_id, FieldInstanceInterface $instance, EntityDisplayBaseInterface $entity_display, array $form, array &$form_state) {
     $field_row = parent::buildFieldRow($field_id, $instance, $entity_display, $form, $form_state);
 
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Plugin/Derivative/FieldUiLocalTask.php b/core/modules/field_ui/lib/Drupal/field_ui/Plugin/Derivative/FieldUiLocalTask.php
index 3e15548..a75a495 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Plugin/Derivative/FieldUiLocalTask.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Plugin/Derivative/FieldUiLocalTask.php
@@ -173,6 +173,9 @@ public function getDerivativeDefinitions(array $base_plugin_definition) {
 
   /**
    * Alters the tab_root_id definition for field_ui local tasks.
+   *
+   * @param array $local_tasks
+   *   An array of local tasks plugin definitions, keyed by plugin ID.
    */
   public function alterLocalTasks(&$local_tasks) {
     foreach ($this->entityManager->getDefinitions() as $entity_type => $entity_info) {