diff --git a/core/modules/ckeditor/src/Tests/CKEditorAdminTest.php b/core/modules/ckeditor/src/Tests/CKEditorAdminTest.php
index ca1954f..09e2988 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorAdminTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorAdminTest.php
@@ -218,6 +218,22 @@ function testExistingFormat() {
     $editor = entity_load('editor', 'filtered_html');
     $this->assertTrue($editor instanceof Editor, 'An Editor config entity exists.');
     $this->assertIdentical($expected_settings, $editor->getSettings());
+
+    $this->drupalGet('admin/config/content/formats/add');
+    // Now attempt to add another filter format with the same editor and same
+    // machine name.
+    $edit = array(
+      'format' => 'filtered_html',
+      'name' => 'Filtered HTML',
+      'editor[editor]' => 'ckeditor',
+    );
+    $this->drupalPostAjaxForm(NULL, $edit, 'editor_configure');
+    $this->assertResponse(200);
+    $edit += [
+      'editor[settings][plugins][llama_contextual_and_button][ultra_llama_mode]' => '1',
+    ];
+    $this->drupalPostForm(NULL, $edit, t('Save configuration'));
+    $this->assertResponse(200);
   }
 
   /**