diff --git a/uuid.js b/uuid.js
index 6598c9b3..4198ca84 100644
--- a/uuid.js
+++ b/uuid.js
@@ -18,7 +18,7 @@
   // Node.js crypto-based RNG - http://nodejs.org/docs/v0.6.2/api/crypto.html
   //
   // Moderately fast, high quality
-  if ('function' === typeof require) {
+  if ('undefined' === typeof window && 'function' === typeof require) {
     try {
       var _rb = require('crypto').randomBytes;
       _nodeRNG = _rng = _rb && function() {return _rb(16);};