diff --git a/is-number-object.js b/is-number-object.js
index 5147256..142ae34 100644
--- a/is-number-object.js
+++ b/is-number-object.js
@@ -1,5 +1,8 @@
 'use strict';
 
+/* Derived from `is-number-object 1.0.7`, under MIT license, (c) 2015 Jordan Harband.
+   This version removes the try/catch for performance reasons, and replaces it with a test that unfortunately does not work on cross-realm values, pending an upstream fix. */
+
 var numToStr = Number.prototype.toString;
 
 var toStr = Object.prototype.toString;