diff --git a/js/gdm/realmd.js b/js/gdm/realmd.js
index 913fdd3be..758496820 100644
--- a/js/gdm/realmd.js
+++ b/js/gdm/realmd.js
@@ -21,6 +21,7 @@ var Manager = class {
                                            '/org/freedesktop/realmd',
                                            this._reloadRealms.bind(this));
         this._realms = {};
+        this._loginFormat = null;
 
         this._signalId = this._aggregateProvider.connect('g-properties-changed',
             (proxy, properties) => {
@@ -86,7 +87,7 @@ var Manager = class {
     }
 
     get loginFormat() {
-        if (this._loginFormat !== undefined)
+        if (this._loginFormat)
             return this._loginFormat;
 
         this._updateLoginFormat();