diff --git a/data/theme/gnome-shell.css b/data/theme/gnome-shell.css
index a229653bd..6f45cfffe 100644
--- a/data/theme/gnome-shell.css
+++ b/data/theme/gnome-shell.css
@@ -1948,10 +1948,12 @@ StScrollBar StButton#vhandle:hover
     padding-bottom: 8px;
 }
 
-/* intentionally left transparent to avoid dialog changing size */
+.hidden {
+    color: rgba(0,0,0,0);
+}
+
 .prompt-dialog-null-label {
     font-size: 10pt;
-    color: rgba(0,0,0,0);
     padding-bottom: 8px;
 }
 
diff --git a/js/ui/polkitAuthenticationAgent.js b/js/ui/polkitAuthenticationAgent.js
index 6a05e1a0e..203863174 100644
--- a/js/ui/polkitAuthenticationAgent.js
+++ b/js/ui/polkitAuthenticationAgent.js
@@ -167,6 +167,7 @@ const AuthenticationDialog = new Lang.Class({
          */
         this._nullMessageLabel = new St.Label({ style_class: 'prompt-dialog-null-label',
                                                 text: 'abc'});
+        this._nullMessageLabel.add_style_class_name('hidden');
         this._nullMessageLabel.clutter_text.ellipsize = Pango.EllipsizeMode.NONE;
         this._nullMessageLabel.clutter_text.line_wrap = true;
         messageBox.add(this._nullMessageLabel);