diff --git a/Gruntfile.js b/Gruntfile.js
index b7f0f3b3..ef66d7e8 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -118,6 +118,13 @@ module.exports = function(grunt) {
         cwd: 'node_modules/',
         src: ['mocha/mocha.css', 'mocha/mocha.js', 'chai/chai.js', 'es6-promise/dist/promise*.js'],
         dest: 'test/lib/'
+      },
+      polyfill: {
+        expand: true,
+        flatten: true,
+        cwd: 'node_modules/',
+        src: ['es6-promise/dist/promise*.js'],
+        dest: 'dist/'
       }
     },
     clean: ['dist/'],
diff --git a/src/worker/worker.js b/src/worker/worker.js
index 5e6baeb9..7f122b00 100644
--- a/src/worker/worker.js
+++ b/src/worker/worker.js
@@ -17,6 +17,32 @@
 
 window = {}; // to make UMD bundles work
 
+// Mozilla bind polyfill because phantomjs is stupid
+if (!Function.prototype.bind) {
+  Function.prototype.bind = function(oThis) {
+    if (typeof this !== "function") {
+      // closest thing possible to the ECMAScript 5 internal IsCallable function
+      throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
+    }
+
+    var aArgs = Array.prototype.slice.call(arguments, 1),
+        fToBind = this,
+        FNOP = function() {},
+        fBound = function() {
+          return fToBind.apply(this instanceof FNOP && oThis ? this : oThis, aArgs.concat(Array.prototype.slice.call(arguments)));
+        };
+
+    FNOP.prototype = this.prototype;
+    fBound.prototype = new FNOP();
+
+    return fBound;
+  };
+}
+
+if (typeof Promise === 'undefined') {
+  // promises polyfill
+  importScripts('promise-1.0.0.js');
+}
 importScripts('openpgp.js');
 
 var MIN_SIZE_RANDOM_BUFFER = 40000;