diff --git a/packages/portal/src/index.js b/packages/portal/src/index.js
index 3144f8e..d667042 100644
--- a/packages/portal/src/index.js
+++ b/packages/portal/src/index.js
@@ -42,7 +42,7 @@ export function WorkerPortal(context, worker, serialize) {
 		_worker.postMessage(_serialize(type, destination, id, params));
 	}
 
-	_worker.onmessage = function dispatcher(evt) {
+	function dispatcher(evt) {
 		let data;
 		try {
 			data = JSON.parse(evt.data);
@@ -80,7 +80,8 @@ export function WorkerPortal(context, worker, serialize) {
 		} else {
 			_resolve(thennable);
 		}
-	};
+	}
+
 	function injectionPointFactory(fnId, fnName, callbackFactory) {
 		return () =>
 			new Promise((resolve, reject) => {
@@ -102,6 +103,8 @@ export function WorkerPortal(context, worker, serialize) {
 		};
 	}
 
+	_worker.addEventListener('message', dispatcher);
+
 	return isWorker()
 		? new Promise(resolve => {
 				contextIndex.splice(0, 0, '__init');