diff --git a/browser-atob.js b/browser-atob.js
index d71b990..95ff45b 100644
--- a/browser-atob.js
+++ b/browser-atob.js
@@ -1,2 +1,32 @@
-// do nothing window.atob already exists
-// NOTE: iOS Web Worker and other weird environments may not have atob
+(function (w) {
+  "use strict";
+
+  var a2b = w.atob;
+
+  function atob(str) {
+    // normal window
+    if ('function' === typeof a2b) {
+      return a2b(a2b);
+    }
+    // browserify (web worker)
+    else if ('function' === typeof Buffer) {
+      return new Buffer(str, 'base64').toString('binary');
+    }
+    // ios web worker with base64js
+    else if ('object' === typeof w.base64js) {
+      // bufferToBinaryString
+      // https://github.com/coolaj86/unibabel-js/blob/master/index.js#L50
+      var buf = w.base64js.b64ToByteArray(str);
+
+      return Array.prototype.map.call(buf, function (ch) {
+        return String.fromCharCode(ch);
+      }).join('');
+    }
+    // ios web worker without base64js
+    else {
+      throw new Error("you're probably in an ios webworker. please include use beatgammit's base64-js");
+    }
+  }
+
+  w.atob = atob;
+}(window));