diff --git a/plugins/acl/acl.js b/plugins/acl/acl.js
index 14634534e..e6a84ff73 100644
--- a/plugins/acl/acl.js
+++ b/plugins/acl/acl.js
@@ -353,6 +353,7 @@ rcube_webmail.prototype.acl_init_form = function(id)
         id ? this.gettext('acl.editperms') : this.gettext('acl.newuser'),
         buttons,
         {
+            button_classes: ['mainaction'],
             modal: true,
             closeOnEscape: true,
             close: function(e, ui) {