Index: wp-includes/nav-menu.php
===================================================================
--- wp-includes/nav-menu.php	(revision 23454)
+++ wp-includes/nav-menu.php	(working copy)
@@ -127,7 +127,8 @@
  */
 
 function get_nav_menu_locations() {
-	return get_theme_mod( 'nav_menu_locations' );
+	$locations = get_theme_mod( 'nav_menu_locations' );
+	return empty( $locations ) || ! is_array( $locations ) ? array() : $locations;
 }
 
 /**