diff --git a/lib/user.php b/lib/user.php
index 3029ec1acc1..2b4e367ab70 100644
--- a/lib/user.php
+++ b/lib/user.php
@@ -345,6 +345,7 @@ class OC_User {
 	 * @return boolean
 	 */
 	public static function userExists($uid){
+		static $user_exists_checked = null;
 		if (!is_null($user_exists_checked)) {
 			return $user_exists_checked;
 		}