diff --git a/core/lib/Drupal/Core/Menu/MenuLinkManager.php b/core/lib/Drupal/Core/Menu/MenuLinkManager.php
index 106407b..dc20367 100644
--- a/core/lib/Drupal/Core/Menu/MenuLinkManager.php
+++ b/core/lib/Drupal/Core/Menu/MenuLinkManager.php
@@ -351,8 +351,11 @@ public function loadLinksByRoute($route_name, array $route_parameters = array(),
    * {@inheritdoc}
    */
   public function addDefinition($id, array $definition) {
-    if ($this->treeStorage->load($id) || $id === '') {
-      throw new PluginException("The ID $id already exists as a plugin definition or is not valid");
+    if ($this->treeStorage->load($id)) {
+      throw new PluginException("The menu link ID $id already exists as a plugin definition.");
+    }
+    elseif ($id === '') {
+      throw new PluginException("The menu link ID can not be empty.");
     }
     // Add defaults, so there is no requirement to specify everything.
     $this->processDefinition($definition, $id);