diff --git a/core/modules/path/path.module b/core/modules/path/path.module
index 1d638ad..b7ce115 100644
--- a/core/modules/path/path.module
+++ b/core/modules/path/path.module
@@ -179,7 +179,17 @@ function path_form_element_validate($element, &$form_state, $complete_form) {
     $query->addExpression('1');
     $query->range(0, 1);
     if ($query->execute()->fetchField()) {
-      form_error($element, t('The alias is already in use.'));
+      form_error($element, t('The URL alias "@alias" is already in use.', array('@alias' => $path['alias'])));
+    }
+
+    // Ensure that the alias does not explicitly override a menu_router item.
+    $query = db_select('menu_router')
+      ->condition('path', $path['alias']);
+    $query->addExpression('1');
+    $query->range(0, 1);
+
+    if ($query->execute()->fetchField()) {
+      form_error($element, t('The URL alias "@alias" is already in use by the system.', array('@alias' => $path['alias'])));
     }
   }
 }