diff --git a/index.js b/index.js
index 8bfc1ad..350cd4b 100644
--- a/index.js
+++ b/index.js
@@ -2,7 +2,7 @@
   "use strict";
 
   function btoa(str) {
-    return new Buffer(str, 'utf8').toString('base64');
+    return new Buffer(str, 'binary').toString('base64');
   }
 
   module.exports = btoa;