diff --git a/src/definitions/modules/progress.js b/src/definitions/modules/progress.js
index f7b79b970..af38f7b0b 100644
--- a/src/definitions/modules/progress.js
+++ b/src/definitions/modules/progress.js
@@ -453,7 +453,7 @@ $.fn.progress = function(parameters) {
             $bar.one(transitionEnd + eventNamespace, animationCallback);
             animating = true;
             module.interval = setInterval(function() {
-              let
+              var
                 isInDOM = $.contains(document.documentElement, element)
               ;
               if(!isInDOM) {