diff --git a/gui/default/syncthing/core/syncthingController.js b/gui/default/syncthing/core/syncthingController.js
index fa565b8b8..692007351 100755
--- a/gui/default/syncthing/core/syncthingController.js
+++ b/gui/default/syncthing/core/syncthingController.js
@@ -2808,7 +2808,7 @@ angular.module('syncthing.core')
 
         $scope.themeName = function (theme) {
             var translation = $translate.instant("theme-name-" + theme);
-            if (translation.startsWith("theme-name-")) {
+            if (translation.indexOf("theme-name-") == 0) {
                 // Fall back to simple Title Casing on missing translation
                 translation = theme.toLowerCase().replace(/(?:^|\s)\S/g, function (a) {
                     return a.toUpperCase();