diff --git a/js/lib/id/util.js b/js/lib/id/util.js
index 01c2ffdb0..c038fdfd6 100644
--- a/js/lib/id/util.js
+++ b/js/lib/id/util.js
@@ -157,7 +157,7 @@
     }
 
     /* eslint-disable no-proto */
-    const getPrototypeOf = Object.getPrototypeOf || function(obj) { return obj.__proto__; };
+    var getPrototypeOf = Object.getPrototypeOf || function(obj) { return obj.__proto__; };
     /* eslint-enable no-proto */
 
     function asyncMap(inputs, func, callback) {
diff --git a/modules/util/util.js b/modules/util/util.js
index a7020d7a5..db44f3627 100644
--- a/modules/util/util.js
+++ b/modules/util/util.js
@@ -151,7 +151,7 @@ export function fastMouse(container) {
 }
 
 /* eslint-disable no-proto */
-export const getPrototypeOf = Object.getPrototypeOf || function(obj) { return obj.__proto__; };
+export var getPrototypeOf = Object.getPrototypeOf || function(obj) { return obj.__proto__; };
 /* eslint-enable no-proto */
 
 export function asyncMap(inputs, func, callback) {