diff --git a/LICENSE.txt b/LICENSE.txt
index e9a3e15e..a8d24e39 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -43,6 +43,8 @@ licenses (all MPL 2.0 compatible):
 
     vendor/browser-es-module-loader: MIT
 
+    vendor/promise.js       : MIT
+
 Any other files not mentioned above are typically marked with
 a copyright/license header at the top of the file. The default noVNC
 license is MPL-2.0.
diff --git a/utils/use_require.js b/utils/use_require.js
index f0383d09..8522256b 100755
--- a/utils/use_require.js
+++ b/utils/use_require.js
@@ -14,24 +14,29 @@ program
     .parse(process.argv);
 
 // the various important paths
-var main_path = path.resolve(__dirname, '..');
-var core_path = path.resolve(__dirname, '..', 'core');
-var app_path = path.resolve(__dirname, '..', 'app');
-var vendor_path = path.resolve(__dirname, '..', 'vendor');
-var out_dir_base = path.resolve(__dirname, '..', 'build');
-var lib_dir_base = path.resolve(__dirname, '..', 'lib');
+const paths = {
+    main: path.resolve(__dirname, '..'),
+    core: path.resolve(__dirname, '..', 'core'),
+    app: path.resolve(__dirname, '..', 'app'),
+    vendor: path.resolve(__dirname, '..', 'vendor'),
+    out_dir_base: path.resolve(__dirname, '..', 'build'),
+    lib_dir_base: path.resolve(__dirname, '..', 'lib'),
+};
 
 const no_copy_files = new Set([
     // skip these -- they don't belong in the processed application
-    path.join(vendor_path, 'sinon.js'),
-    path.join(vendor_path, 'browser-es-module-loader'),
+    path.join(paths.vendor, 'sinon.js'),
+    path.join(paths.vendor, 'browser-es-module-loader'),
+    path.join(paths.vendor, 'promise.js'),
 ]);
 
 const no_transform_files = new Set([
     // don't transform this -- we want it imported as-is to properly catch loading errors
-    path.join(app_path, 'error-handler.js'),
+    path.join(paths.app, 'error-handler.js'),
 ]);
 
+no_copy_files.forEach((file) => no_transform_files.add(file));
+
 // walkDir *recursively* walks directories trees,
 // calling the callback for all normal files found.
 var walkDir = function (base_path, cb, filter) {
@@ -55,7 +60,7 @@ var walkDir = function (base_path, cb, filter) {
 var transform_html = function (new_script) {
     // write out the modified vnc.html file that works with the bundle
     var src_html_path = path.resolve(__dirname, '..', 'vnc.html');
-    var out_html_path = path.resolve(out_dir_base, 'vnc.html');
+    var out_html_path = path.resolve(paths.out_dir_base, 'vnc.html');
     fs.readFile(src_html_path, (err, contents_raw) => {
         if (err) { throw err; }
 
@@ -92,10 +97,10 @@ var make_lib_files = function (import_format, source_maps, with_app_dir) {
 
     var in_path;
     if (with_app_dir) {
-        var out_path_base = out_dir_base;
-        in_path = main_path;
+        var out_path_base = paths.out_dir_base;
+        in_path = paths.main;
     } else {
-        var out_path_base = lib_dir_base;
+        var out_path_base = paths.lib_dir_base;
     }
 
     fse.ensureDirSync(out_path_base);
@@ -144,11 +149,15 @@ var make_lib_files = function (import_format, source_maps, with_app_dir) {
         });
     };
 
-    walkDir(core_path, handleDir.bind(null, true, in_path || core_path), (filename, stats) => !no_copy_files.has(filename));
-    walkDir(vendor_path, handleDir.bind(null, true, in_path || main_path), (filename, stats) => !no_copy_files.has(filename));
+    if (with_app_dir && helper && helper.noCopyOverride) {
+        helper.noCopyOverride(paths, no_copy_files);
+    }
+
+    walkDir(paths.core, handleDir.bind(null, true, in_path || paths.core), (filename, stats) => !no_copy_files.has(filename));
+    walkDir(paths.vendor, handleDir.bind(null, true, in_path || paths.main), (filename, stats) => !no_copy_files.has(filename));
 
     if (with_app_dir) {
-        walkDir(app_path, handleDir.bind(null, false, in_path || app_path), (filename, stats) => !no_copy_files.has(filename));
+        walkDir(paths.app, handleDir.bind(null, false, in_path || paths.app), (filename, stats) => !no_copy_files.has(filename));
 
         const out_app_path = path.join(out_path_base, 'app.js');
         if (helper && helper.appWriter) {
diff --git a/utils/use_require_helpers.js b/utils/use_require_helpers.js
index b8ac46e6..990fb4df 100644
--- a/utils/use_require_helpers.js
+++ b/utils/use_require_helpers.js
@@ -11,6 +11,7 @@ module.exports = {
             console.log(`Please place RequireJS in ${path.join(base_out_path, 'require.js')}`);
             return `<script src="require.js" data-main="${path.relative(base_out_path, out_path)}"></script>`;
         },
+        noCopyOverride: () => {},
     },
     'commonjs': {
         optionsOverride: (opts) => {   
@@ -23,12 +24,17 @@ module.exports = {
             b.bundle().pipe(fs.createWriteStream(out_path));
             return `<script src="${path.relative(base_out_path, out_path)}"></script>`;
         },
+        noCopyOverride: () => {},
     },
     'systemjs': {
         appWriter: (base_out_path, out_path) => {
             fs.writeFile(out_path, 'SystemJS.import("./app/ui.js");', (err) => { if (err) throw err; });
             console.log(`Please place SystemJS in ${path.join(base_out_path, 'system-production.js')}`);
-            return `<script src="system-production.js"></script>\n<script src="${path.relative(base_out_path, out_path)}"></script>`;
+            return `<script src="vendor/promise.js"></script>
+<script src="system-production.js"></script>\n<script src="${path.relative(base_out_path, out_path)}"></script>`;
+        },
+        noCopyOverride: (paths, no_copy_files) => {
+            no_copy_files.delete(path.join(paths.vendor, 'promise.js'));
         },
     },
     'umd': {
diff --git a/vendor/browser-es-module-loader/dist/browser-es-module-loader.js b/vendor/browser-es-module-loader/dist/browser-es-module-loader.js
index 0d22bab2..8d3a2eea 100644
--- a/vendor/browser-es-module-loader/dist/browser-es-module-loader.js
+++ b/vendor/browser-es-module-loader/dist/browser-es-module-loader.js
@@ -1343,9 +1343,9 @@ WorkerPool.prototype = {
   },
 
   _stop: function () {
-    for (let wrkr of this._workers) {
+    this._workers.forEach(function(wrkr) {
       wrkr.terminate();
-    }
+    });
   }
 };
 
diff --git a/vendor/browser-es-module-loader/src/browser-es-module-loader.js b/vendor/browser-es-module-loader/src/browser-es-module-loader.js
index a9d72097..6154e446 100644
--- a/vendor/browser-es-module-loader/src/browser-es-module-loader.js
+++ b/vendor/browser-es-module-loader/src/browser-es-module-loader.js
@@ -183,9 +183,9 @@ WorkerPool.prototype = {
   },
 
   _stop: function () {
-    for (let wrkr of this._workers) {
+    this._workers.forEach(function(wrkr) {
       wrkr.terminate();
-    }
+    });
   }
 };
 
diff --git a/vendor/promise.js b/vendor/promise.js
new file mode 100644
index 00000000..62843432
--- /dev/null
+++ b/vendor/promise.js
@@ -0,0 +1,255 @@
+/* Copyright (c) 2014 Taylor Hakes
+ * Copyright (c) 2014 Forbes Lindesay
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+(function (root) {
+
+  // Store setTimeout reference so promise-polyfill will be unaffected by
+  // other code modifying setTimeout (like sinon.useFakeTimers())
+  var setTimeoutFunc = setTimeout;
+
+  function noop() {}
+  
+  // Polyfill for Function.prototype.bind
+  function bind(fn, thisArg) {
+    return function () {
+      fn.apply(thisArg, arguments);
+    };
+  }
+
+  function Promise(fn) {
+    if (typeof this !== 'object') throw new TypeError('Promises must be constructed via new');
+    if (typeof fn !== 'function') throw new TypeError('not a function');
+    this._state = 0;
+    this._handled = false;
+    this._value = undefined;
+    this._deferreds = [];
+
+    doResolve(fn, this);
+  }
+
+  function handle(self, deferred) {
+    while (self._state === 3) {
+      self = self._value;
+    }
+    if (self._state === 0) {
+      self._deferreds.push(deferred);
+      return;
+    }
+    self._handled = true;
+    Promise._immediateFn(function () {
+      var cb = self._state === 1 ? deferred.onFulfilled : deferred.onRejected;
+      if (cb === null) {
+        (self._state === 1 ? resolve : reject)(deferred.promise, self._value);
+        return;
+      }
+      var ret;
+      try {
+        ret = cb(self._value);
+      } catch (e) {
+        reject(deferred.promise, e);
+        return;
+      }
+      resolve(deferred.promise, ret);
+    });
+  }
+
+  function resolve(self, newValue) {
+    try {
+      // Promise Resolution Procedure: https://github.com/promises-aplus/promises-spec#the-promise-resolution-procedure
+      if (newValue === self) throw new TypeError('A promise cannot be resolved with itself.');
+      if (newValue && (typeof newValue === 'object' || typeof newValue === 'function')) {
+        var then = newValue.then;
+        if (newValue instanceof Promise) {
+          self._state = 3;
+          self._value = newValue;
+          finale(self);
+          return;
+        } else if (typeof then === 'function') {
+          doResolve(bind(then, newValue), self);
+          return;
+        }
+      }
+      self._state = 1;
+      self._value = newValue;
+      finale(self);
+    } catch (e) {
+      reject(self, e);
+    }
+  }
+
+  function reject(self, newValue) {
+    self._state = 2;
+    self._value = newValue;
+    finale(self);
+  }
+
+  function finale(self) {
+    if (self._state === 2 && self._deferreds.length === 0) {
+      Promise._immediateFn(function() {
+        if (!self._handled) {
+          Promise._unhandledRejectionFn(self._value);
+        }
+      });
+    }
+
+    for (var i = 0, len = self._deferreds.length; i < len; i++) {
+      handle(self, self._deferreds[i]);
+    }
+    self._deferreds = null;
+  }
+
+  function Handler(onFulfilled, onRejected, promise) {
+    this.onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : null;
+    this.onRejected = typeof onRejected === 'function' ? onRejected : null;
+    this.promise = promise;
+  }
+
+  /**
+   * Take a potentially misbehaving resolver function and make sure
+   * onFulfilled and onRejected are only called once.
+   *
+   * Makes no guarantees about asynchrony.
+   */
+  function doResolve(fn, self) {
+    var done = false;
+    try {
+      fn(function (value) {
+        if (done) return;
+        done = true;
+        resolve(self, value);
+      }, function (reason) {
+        if (done) return;
+        done = true;
+        reject(self, reason);
+      });
+    } catch (ex) {
+      if (done) return;
+      done = true;
+      reject(self, ex);
+    }
+  }
+
+  Promise.prototype['catch'] = function (onRejected) {
+    return this.then(null, onRejected);
+  };
+
+  Promise.prototype.then = function (onFulfilled, onRejected) {
+    var prom = new (this.constructor)(noop);
+
+    handle(this, new Handler(onFulfilled, onRejected, prom));
+    return prom;
+  };
+
+  Promise.all = function (arr) {
+    var args = Array.prototype.slice.call(arr);
+
+    return new Promise(function (resolve, reject) {
+      if (args.length === 0) return resolve([]);
+      var remaining = args.length;
+
+      function res(i, val) {
+        try {
+          if (val && (typeof val === 'object' || typeof val === 'function')) {
+            var then = val.then;
+            if (typeof then === 'function') {
+              then.call(val, function (val) {
+                res(i, val);
+              }, reject);
+              return;
+            }
+          }
+          args[i] = val;
+          if (--remaining === 0) {
+            resolve(args);
+          }
+        } catch (ex) {
+          reject(ex);
+        }
+      }
+
+      for (var i = 0; i < args.length; i++) {
+        res(i, args[i]);
+      }
+    });
+  };
+
+  Promise.resolve = function (value) {
+    if (value && typeof value === 'object' && value.constructor === Promise) {
+      return value;
+    }
+
+    return new Promise(function (resolve) {
+      resolve(value);
+    });
+  };
+
+  Promise.reject = function (value) {
+    return new Promise(function (resolve, reject) {
+      reject(value);
+    });
+  };
+
+  Promise.race = function (values) {
+    return new Promise(function (resolve, reject) {
+      for (var i = 0, len = values.length; i < len; i++) {
+        values[i].then(resolve, reject);
+      }
+    });
+  };
+
+  // Use polyfill for setImmediate for performance gains
+  Promise._immediateFn = (typeof setImmediate === 'function' && function (fn) { setImmediate(fn); }) ||
+    function (fn) {
+      setTimeoutFunc(fn, 0);
+    };
+
+  Promise._unhandledRejectionFn = function _unhandledRejectionFn(err) {
+    if (typeof console !== 'undefined' && console) {
+      console.warn('Possible Unhandled Promise Rejection:', err); // eslint-disable-line no-console
+    }
+  };
+
+  /**
+   * Set the immediate function to execute callbacks
+   * @param fn {function} Function to execute
+   * @deprecated
+   */
+  Promise._setImmediateFn = function _setImmediateFn(fn) {
+    Promise._immediateFn = fn;
+  };
+
+  /**
+   * Change the function to execute on unhandled rejection
+   * @param {function} fn Function to execute on unhandled rejection
+   * @deprecated
+   */
+  Promise._setUnhandledRejectionFn = function _setUnhandledRejectionFn(fn) {
+    Promise._unhandledRejectionFn = fn;
+  };
+  
+  if (typeof module !== 'undefined' && module.exports) {
+    module.exports = Promise;
+  } else if (!root.Promise) {
+    root.Promise = Promise;
+  }
+
+})(this);
diff --git a/vnc.html b/vnc.html
index 10cc1430..02fe5c69 100644
--- a/vnc.html
+++ b/vnc.html
@@ -63,6 +63,8 @@
     <script type="text/javascript" src="app/error-handler.js"></script>
 
     <!-- begin scripts -->
+    <!-- promise polyfills promises for IE11 -->
+    <script src="vendor/promise.js"></script>
     <script src="vendor/browser-es-module-loader/dist/browser-es-module-loader.js"></script>
     <script type="module" src="app/ui.js"></script>
     <!-- end scripts -->