diff --git a/packages/portal/src/index.js b/packages/portal/src/index.js
index ac61314..ab3f88e 100644
--- a/packages/portal/src/index.js
+++ b/packages/portal/src/index.js
@@ -42,7 +42,9 @@ export function WorkerPortal(context, worker, isSlave, serialize) {
 		} catch (e) {
 			data = evt.data;
 		}
-		const [type, destination, id, params] = data;
+		const destination = data[1];
+		const id = data[2];
+		const params = data[3];
 
 		function _resolve(value) {
 			post(1, id, 0, value);
@@ -52,7 +54,7 @@ export function WorkerPortal(context, worker, isSlave, serialize) {
 		}
 
 		// If we have received an RPC response, satisfy the promise.
-		if (type) {
+		if (data[0]) {
 			if (responseMap.has(id)) {
 				const responses = responseMap.get(id);
 				responseMap.delete(id);
@@ -121,8 +123,9 @@ export function WorkerPortal(context, worker, isSlave, serialize) {
 		});
 	}
 
-	return injectionPointFactory(0, resolveExternalInterfaceFactory)(contextIndex).then(api => ({
-		...api,
-		_cleanup: injectionPointFactory(1, resolve => resolve(cleanup()))
-	}));
+	return injectionPointFactory(0, resolveExternalInterfaceFactory)(contextIndex).then(api =>
+		Object.assign(api, {
+			_cleanup: injectionPointFactory(1, resolve => resolve(cleanup()))
+		})
+	);
 }