diff --git a/wp-includes/user-functions.php b/wp-includes/user-functions.php
index fd73875958..9e95bee6c7 100644
--- a/wp-includes/user-functions.php
+++ b/wp-includes/user-functions.php
@@ -1102,9 +1102,18 @@ function sanitize_user_field($field, $value, $user_id, $context) {
  *
  * @since 3.0.0
  *
- * @param object $user User object to be cached
+ * @param object|WP_User $user User object to be cached
+ * @return bool|null Returns false on failure.
  */
-function update_user_caches($user) {
+function update_user_caches( $user ) {
+	if ( $user instanceof WP_User ) {
+		if ( ! $user->exists() ) {
+			return false;
+		}
+
+		$user = $user->data;
+	}
+
 	wp_cache_add($user->ID, $user, 'users');
 	wp_cache_add($user->user_login, $user->ID, 'userlogins');
 	wp_cache_add($user->user_email, $user->ID, 'useremail');
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 6e5d5d9c01..bebc61f0b0 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34918';
+$wp_version = '4.4-alpha-34919';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.