diff --git modules/flag/includes/flag.views.inc modules/flag/includes/flag.views.inc
index 4760fec..e4d641f 100644
--- modules/flag/includes/flag.views.inc
+++ modules/flag/includes/flag.views.inc
@@ -81,6 +81,9 @@ function flag_views_data() {
       'handler' => 'views_handler_relationship',
       'label' => t('Flag user'),
     ),
+    'argument' => array(
+      'handler' => 'views_handler_argument_numeric',
+    ),
   );
 
   $data['flag_content']['timestamp'] = array(