diff --git a/wp-admin/nav-menus.php b/wp-admin/nav-menus.php
index cb40158aa..7ca9fc7e0 100644
--- a/wp-admin/nav-menus.php
+++ b/wp-admin/nav-menus.php
@@ -269,6 +269,9 @@ switch ( $action ) {
if ( is_wp_error( $_nav_menu_selected_id ) ) {
$messages[] = '
' . $_nav_menu_selected_id->get_error_message() . '
';
} else {
+ if ( ( $_menu_locations = get_registered_nav_menus() ) && 1 == count( wp_get_nav_menus() ) )
+ set_theme_mod( 'nav_menu_locations', array( key( $_menu_locations ) => $_nav_menu_selected_id ) );
+ unset( $_menu_locations );
$_menu_object = wp_get_nav_menu_object( $_nav_menu_selected_id );
$nav_menu_selected_id = $_nav_menu_selected_id;
$nav_menu_selected_title = $_menu_object->name;