Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 21378)
+++ wp-includes/user.php	(working copy)
@@ -1391,7 +1391,7 @@
  * @uses wp_insert_user() Used to update existing user or add new one if user doesn't exist already
  *
  * @param array $userdata An array of user data.
- * @return int The updated user's ID.
+ * @return int|WP_Error The updated user's ID or a WP_Error object if the user could not be updated.
  */
 function wp_update_user($userdata) {
 	$ID = (int) $userdata['ID'];