diff --git a/index.js b/index.js
index 82b9107..76c17da 100644
--- a/index.js
+++ b/index.js
@@ -13,31 +13,35 @@ function parseJsonSafely(str) {
   }
 }
 
+function onMessage (self, e) {
+  var message = parseJsonSafely(e.data);
+  if (!message) {
+    // Ignore - this message is not for us.
+    return;
+  }
+  var messageId = message[0];
+  var error = message[1];
+  var result = message[2];
+
+  var callback = self._callbacks[messageId];
+
+  if (!callback) {
+    // Ignore - user might have created multiple PromiseWorkers.
+    // This message is not for us.
+    return;
+  }
+
+  delete self._callbacks[messageId];
+  callback(error, result);
+}
+
 function PromiseWorker(worker) {
   var self = this;
   self._worker = worker;
   self._callbacks = {};
 
-  worker.addEventListener('message', function onIncomingMessage(e) {
-    var message = parseJsonSafely(e.data);
-    if (!message) {
-      // Ignore - this message is not for us.
-      return;
-    }
-    var messageId = message[0];
-    var error = message[1];
-    var result = message[2];
-
-    var callback = self._callbacks[messageId];
-
-    if (!callback) {
-      // Ignore - user might have created multiple PromiseWorkers.
-      // This message is not for us.
-      return;
-    }
-
-    delete self._callbacks[messageId];
-    callback(error, result);
+  worker.addEventListener('message', function (e) {
+    self._onMessage(e);
   });
 }
 
@@ -58,7 +62,11 @@ PromiseWorker.prototype.postMessage = function (userMessage) {
     /* istanbul ignore if */
     if (typeof self._worker.controller !== 'undefined') {
       // service worker
-      self._worker.controller.postMessage(jsonMessage);
+      var channel = new MessageChannel();
+      channel.port1.onmessage = function (e) {
+        self._onMessage(e);
+      };
+      self._worker.controller.postMessage(jsonMessage, [channel.port2]);
     } else {
       // web worker
       self._worker.postMessage(jsonMessage);
diff --git a/register.js b/register.js
index a65f738..86b31b1 100644
--- a/register.js
+++ b/register.js
@@ -16,7 +16,7 @@ function registerPromiseWorker(callback) {
     function postMessage(msg) {
       /* istanbul ignore if */
       if (typeof self.postMessage !== 'function') { // service worker
-        e.source.postMessage(msg);
+        e.ports[0].postMessage(msg);
       } else { // web worker
         self.postMessage(msg);
       }