diff --git a/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php b/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
index ba054a6..08ada45 100644
--- a/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
+++ b/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
@@ -234,20 +234,15 @@ public function settingsForm(array $form, FormStateInterface $form_state, Editor
   /**
    * {@inheritdoc}
    */
-  public function settingsFormSubmit(array $form, FormStateInterface $form_state) {
-    // Modify the toolbar settings by reference. The values in
-    // $form_state->getValue(array('editor', 'settings')) will be saved directly
-    // by editor_form_filter_admin_format_submit().
-    $toolbar_settings = &$form_state->getValue(array('editor', 'settings', 'toolbar'));
-
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
     // The rows key is not built into the form structure, so decode the button
     // groups data into this new key and remove the button_groups key.
-    $toolbar_settings['rows'] = json_decode($toolbar_settings['button_groups'], TRUE);
-    unset($toolbar_settings['button_groups']);
+    $form_state->setValue(['toolbar', 'rows'], json_decode($form_state->getValue(['toolbar', 'button_groups']), TRUE));
+    $form_state->unsetValue(['toolbar', 'button_groups']);
 
     // Remove the plugin settings' vertical tabs state; no need to save that.
-    if ($form_state->hasValue(array('editor', 'settings', 'plugins'))) {
-      $form_state->unsetValue(array('editor', 'settings', 'plugin_settings'));
+    if ($form_state->hasValue('plugins')) {
+      $form_state->unsetValue('plugin_settings');
     }
   }
 
diff --git a/core/modules/editor/src/Plugin/EditorBase.php b/core/modules/editor/src/Plugin/EditorBase.php
index bd429d1..3456e44 100644
--- a/core/modules/editor/src/Plugin/EditorBase.php
+++ b/core/modules/editor/src/Plugin/EditorBase.php
@@ -3,6 +3,7 @@
 namespace Drupal\editor\Plugin;
 
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformStateInterface;
 use Drupal\Core\Plugin\PluginBase;
 use Drupal\editor\Entity\Editor;
 
@@ -61,6 +62,9 @@ public function settingsFormSubmit(array $form, FormStateInterface $form_state)
    * {@inheritdoc}
    */
   public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    if ($form_state instanceof SubformStateInterface) {
+      $form_state = $form_state->getCompleteFormState();
+    }
     return $this->settingsForm($form, $form_state, $form_state->get('editor'));
   }
 
@@ -68,6 +72,9 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
    * {@inheritdoc}
    */
   public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
+    if ($form_state instanceof SubformStateInterface) {
+      $form_state = $form_state->getCompleteFormState();
+    }
     return $this->settingsFormValidate($form, $form_state);
   }
 
@@ -75,6 +82,9 @@ public function validateConfigurationForm(array &$form, FormStateInterface $form
    * {@inheritdoc}
    */
   public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    if ($form_state instanceof SubformStateInterface) {
+      $form_state = $form_state->getCompleteFormState();
+    }
     return $this->settingsFormSubmit($form, $form_state);
   }