diff --git a/lib/gallery.dialog.js b/lib/gallery.dialog.js
index 6d986aa0..fc66323e 100644
--- a/lib/gallery.dialog.js
+++ b/lib/gallery.dialog.js
@@ -98,6 +98,8 @@ function openDialog(element, on_success) {
 }
 
 function on_form_loaded() {
+  // Should be defined (and localized) in the theme
+  MSG_CANCEL = MSG_CANCEL || 'Cancel';
   var eCancel = '<a href="javascript: closeDialog()" class="gCancel">' + MSG_CANCEL + '</a>';
   if ($("#gDialog .submit").length) {
     $("#gDialog .submit").addClass("ui-state-default ui-corner-all");
diff --git a/themes/admin_default/views/admin.html.php b/themes/admin_default/views/admin.html.php
index fed1afe6..36deea9e 100644
--- a/themes/admin_default/views/admin.html.php
+++ b/themes/admin_default/views/admin.html.php
@@ -21,6 +21,10 @@
    <?= $theme->script("lib/jquery.form.js") ?>
    <?= $theme->script("lib/jquery-ui.js") ?>
    <?= $theme->script("lib/gallery.common.js") ?>
+   <? /* MSG_CANCEL is required by gallery.dialog.js */ ?>
+   <script type="text/javascript">
+   var MSG_CANCEL = "<?= t('Cancel') ?>";
+   </script>
    <?= $theme->script("lib/gallery.dialog.js") ?>
    <?= $theme->script("lib/superfish/js/superfish.js") ?>
    <?= $theme->theme_script("js/jquery.dropshadow.js") ?>