diff --git a/src/objects/now.js b/src/objects/now.js
index 66a7641..307f682 100644
--- a/src/objects/now.js
+++ b/src/objects/now.js
@@ -1,6 +1,7 @@
 let now;
 
 // Include a performance.now polyfill.
+// source https://github.com/tweenjs/tween.js/blob/master/src/Now.ts
 // In node.js, use process.hrtime.
 // eslint-disable-next-line
 // @ts-ignore