diff --git a/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php
index 3728790..72ab6eb 100644
--- a/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php
+++ b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php
@@ -114,8 +114,8 @@ public function getConfig(Editor $editor) {
 
     // Add the format_tags setting, if its button is enabled.
     $toolbar_buttons = CKEditorPluginManager::getEnabledButtons($editor);
-    if (in_array('Format', $toolbar_buttons)) {
-      $config['format_tags'] = $this->generateFormatTagsSetting($editor);
+    if (in_array('Format', $toolbar_buttons) && $format_string = $this->generateFormatTagsSetting($editor)) {
+      $config['format_tags'] = $format_string;
     }
 
     return $config;
@@ -342,14 +342,15 @@ public function getButtons() {
    * @param \Drupal\editor\Entity\Editor $editor
    *   A configured text editor object.
    *
-   * @return array
-   *   An array containing the "format_tags" configuration.
+   * @return string|false
+   *   A string containing the "format_tags" configuration or FALSE if the
+   *   editor has not an associated filter format.
    */
   protected function generateFormatTagsSetting(Editor $editor) {
     // When no text format is associated yet, assume no tag is allowed.
     // @see \Drupal\Editor\EditorInterface::hasAssociatedFilterFormat()
     if (!$editor->hasAssociatedFilterFormat()) {
-      return array();
+      return FALSE;
     }
 
     $format = $editor->getFilterFormat();