diff --git a/core/lib/Drupal/Core/Menu/Form/MenuLinkDefaultForm.php b/core/lib/Drupal/Core/Menu/Form/MenuLinkDefaultForm.php
index 1062b2b..64438f7 100644
--- a/core/lib/Drupal/Core/Menu/Form/MenuLinkDefaultForm.php
+++ b/core/lib/Drupal/Core/Menu/Form/MenuLinkDefaultForm.php
@@ -110,6 +110,10 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
       '#type' => 'item',
       '#title' => $this->t('This link is provided by the @name module. The title and path cannot be edited.', array('@name' => $this->moduleHandler->getName($provider))),
     );
+    $form['id'] = array(
+      '#type' => 'value',
+      '#value' => $this->menuLink->getPluginId(),
+    );
     $link = array(
       '#type' => 'link',
       '#title' => $this->menuLink->getTitle(),
@@ -158,7 +162,11 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
    * {@inheritdoc}
    */
   public function extractFormValues(array &$form, FormStateInterface $form_state) {
-    $new_definition = array();
+    // Start from the complete, original, definition.
+    $new_definition = $this->menuLink->getPluginDefinition();
+    // Since the ID may not be present in the definition used to construct the
+    // plugin, add it here so it's available to any consumers of this method.
+    $new_definition['id'] = $form_state->getValue('id');
     $new_definition['enabled'] = $form_state->getValue('enabled') ? 1 : 0;
     $new_definition['weight'] = (int) $form_state->getValue('weight');
     $new_definition['expanded'] = $form_state->getValue('expanded') ? 1 : 0;