diff --git a/core/modules/menu/lib/Drupal/menu/MenuFormController.php b/core/modules/menu/lib/Drupal/menu/MenuFormController.php
index 525cb4d..8f03f10 100644
--- a/core/modules/menu/lib/Drupal/menu/MenuFormController.php
+++ b/core/modules/menu/lib/Drupal/menu/MenuFormController.php
@@ -35,6 +35,7 @@ public function form(array $form, array &$form_state) {
       '#default_value' => $menu->id(),
       '#maxlength' => MENU_MAX_MENU_NAME_LENGTH_UI,
       '#description' => t('A unique name to construct the URL for the menu. It must only contain lowercase letters, numbers and hyphens.'),
+      '#field_prefix' => $menu->isNew() ? 'menu-' : '',
       '#machine_name' => array(
         'exists' => 'menu_edit_menu_name_exists',
         'source' => array('label'),
@@ -118,10 +119,12 @@ protected function actions(array $form, array &$form_state) {
    * {@inheritdoc}
    */
   public function validate(array $form, array &$form_state) {
+    if ($this->entity->isNew()) {
       // The machine name is validated automatically, we only need to add the
       // 'menu-' prefix here.
       $form_state['values']['id'] = 'menu-' . $form_state['values']['id'];
     }
+  }
 
   /**
    * Submit handler to update the bundle for the default language configuration.
diff --git a/core/modules/menu/lib/Drupal/menu/Tests/MenuLanguageTest.php b/core/modules/menu/lib/Drupal/menu/Tests/MenuLanguageTest.php
index 94421e4..63bfe57 100644
--- a/core/modules/menu/lib/Drupal/menu/Tests/MenuLanguageTest.php
+++ b/core/modules/menu/lib/Drupal/menu/Tests/MenuLanguageTest.php
@@ -68,6 +68,8 @@ function testMenuLanguage() {
     $this->drupalPost('admin/structure/menu/add', $edit, t('Save'));
 
     // Check that the language settings were saved.
+    // The menu name should have been prefixed.
+    $menu_name = 'menu-' . $menu_name;
     $this->assertEqual(entity_load('menu', $menu_name)->langcode, $edit['langcode']);
     $language_settings = language_get_default_configuration('menu_link', $menu_name);
     $this->assertEqual($language_settings['langcode'], 'bb');
@@ -91,7 +93,11 @@ function testMenuLanguage() {
     // Check the link was added with the correct menu link default language.
     $menu_links = entity_load_multiple_by_properties('menu_link', array('link_title' => $link_title));
     $menu_link = reset($menu_links);
-    $this->assertMenuLink($menu_link->id(), array('menu_name' => $menu_name, 'link_path' => $link_path, 'langcode' => 'bb'));
+    $this->assertMenuLink($menu_link->id(), array(
+      'menu_name' => $menu_name,
+      'link_path' => $link_path,
+      'langcode' => 'bb',
+    ));
 
     // Edit menu link default, changing it to cc.
     $edit = array(