diff --git a/src/comlink.ts b/src/comlink.ts
index 06ce2c35..2b24719c 100644
--- a/src/comlink.ts
+++ b/src/comlink.ts
@@ -330,6 +330,8 @@ export function expose(obj: any, ep: Endpoint = self as any) {
             returnValue = undefined;
           }
           break;
+        default:
+          return;
       }
     } catch (value) {
       returnValue = { value, [throwMarker]: 0 };
diff --git a/src/protocol.ts b/src/protocol.ts
index 1bf1cc75..cf3dcb47 100644
--- a/src/protocol.ts
+++ b/src/protocol.ts
@@ -17,6 +17,7 @@ export interface EventSource {
     listener: EventListenerOrEventListenerObject,
     options?: {}
   ): void;
+
   removeEventListener(
     type: string,
     listener: EventListenerOrEventListenerObject,
@@ -34,14 +35,15 @@ export interface PostMessageWithOrigin {
 
 export interface Endpoint extends EventSource {
   postMessage(message: any, transfer?: Transferable[]): void;
+
   start?: () => void;
 }
 
 export const enum WireValueType {
-  RAW,
-  PROXY,
-  THROW,
-  HANDLER,
+  RAW = "RAW",
+  PROXY = "PROXY",
+  THROW = "THROW",
+  HANDLER = "HANDLER",
 }
 
 export interface RawWireValue {
@@ -62,12 +64,12 @@ export type WireValue = RawWireValue | HandlerWireValue;
 export type MessageID = string;
 
 export const enum MessageType {
-  GET,
-  SET,
-  APPLY,
-  CONSTRUCT,
-  ENDPOINT,
-  RELEASE,
+  GET = "GET",
+  SET = "SET",
+  APPLY = "APPLY",
+  CONSTRUCT = "CONSTRUCT",
+  ENDPOINT = "ENDPOINT",
+  RELEASE = "RELEASE",
 }
 
 export interface GetMessage {
diff --git a/tests/fixtures/two-way-iframe.html b/tests/fixtures/two-way-iframe.html
new file mode 100644
index 00000000..e7528624
--- /dev/null
+++ b/tests/fixtures/two-way-iframe.html
@@ -0,0 +1,10 @@
+<script type="module">
+  import * as Comlink from "/base/dist/esm/comlink.mjs";
+
+  const parentEndpoint = Comlink.windowEndpoint(self.parent);
+  const wrappedParent = Comlink.wrap(parentEndpoint);
+
+  Comlink.expose(async (a, b) => {
+    return a + (await wrappedParent(b));
+  }, parentEndpoint);
+</script>
diff --git a/tests/two-way-iframe.comlink.test.js b/tests/two-way-iframe.comlink.test.js
new file mode 100644
index 00000000..ba23b663
--- /dev/null
+++ b/tests/two-way-iframe.comlink.test.js
@@ -0,0 +1,40 @@
+/**
+ * Copyright 2017 Google Inc. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as Comlink from "/base/dist/esm/comlink.mjs";
+
+describe("Comlink across iframes", function () {
+  beforeEach(function () {
+    this.ifr = document.createElement("iframe");
+    this.ifr.sandbox.add("allow-scripts", "allow-same-origin");
+    this.ifr.src = "/base/tests/fixtures/two-way-iframe.html";
+    document.body.appendChild(this.ifr);
+    return new Promise((resolve) => (this.ifr.onload = resolve));
+  });
+
+  afterEach(function () {
+    this.ifr.remove();
+  });
+
+  it("can communicate both ways", async function () {
+    let called = false;
+    const iframe = Comlink.windowEndpoint(this.ifr.contentWindow);
+    Comlink.expose((a) => {
+      called = true;
+      return ++a;
+    }, iframe);
+    const proxy = Comlink.wrap(iframe);
+    expect(await proxy(1, 3)).to.equal(5);
+    expect(called).to.equal(true);
+  });
+});