diff --git a/js/app.js b/js/app.js
index 8f38c291..fb968064 100644
--- a/js/app.js
+++ b/js/app.js
@@ -99,7 +99,7 @@ app = Sammy('#main', function (sam) {
                     c.flash('fail', 'Wrong password');
                 if (xhr.status == 401) {
                     c.flash('fail', 'Wrong password');
-                } else if (typeof xhr.responseJSON !== undefined) {
+                } else if (typeof xhr.responseJSON !== 'undefined') {
                     c.flash('fail', xhr.responseJSON.error);
                 } else {
                     if (uri == '/postinstall') {