diff --git a/lib/user-handler.js b/lib/user-handler.js
index 8f6ddb0d..192073de 100644
--- a/lib/user-handler.js
+++ b/lib/user-handler.js
@@ -370,6 +370,9 @@ class UserHandler {
         this.asyncAuthenticate(username, password, requiredScope, meta)
             .catch(err => callback(err))
             .then(result => {
+                if (!Array.isArray(result)) {
+                    result = [].concat(result || [false, false]);
+                }
                 callback(null, ...result);
             });
     }