diff --git a/index.js b/index.js
index 350cd4b..4c00e7b 100644
--- a/index.js
+++ b/index.js
@@ -2,7 +2,7 @@
   "use strict";
 
   function btoa(str) {
-    return new Buffer(str, 'binary').toString('base64');
+    return new Buffer(str.toString(), 'binary').toString('base64');
   }
 
   module.exports = btoa;