Index: wp-includes/default-widgets.php
===================================================================
--- wp-includes/default-widgets.php	(revision 22376)
+++ wp-includes/default-widgets.php	(working copy)
@@ -1112,7 +1112,7 @@
 		if ( !empty($instance['title']) )
 			echo $args['before_title'] . $instance['title'] . $args['after_title'];
 
-		wp_nav_menu( array( 'fallback_cb' => '', 'menu' => $nav_menu ) );
+		wp_nav_menu( array( 'fallback_cb' => '', 'menu' => $nav_menu, 'theme_location' => $args['id'], ) );
 
 		echo $args['after_widget'];
 	}