diff --git a/README.md b/README.md
index bcfd13a..eb5de3c 100644
--- a/README.md
+++ b/README.md
@@ -63,3 +63,19 @@ delete rpc.handler;
 ```
 
 In Typescript, use `delete (rpc as any).handler`.
+
+## Web worker
+
+The library can also be used with [Web workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers)
+
+```js
+const myWorker = new Worker('worker.js');
+const rpc = connect(window, myWorker, "*");
+```
+
+in `worker.js`
+
+```js
+// ...
+listener.listen(self, "*");
+```
diff --git a/src/index.ts b/src/index.ts
index d5506fa..7d66e99 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,2 +1,2 @@
-export {connect} from "./sender";
+export {connect, Cancelled} from "./sender";
 export {default as Listener} from "./listener";
diff --git a/src/listener.ts b/src/listener.ts
index ee61f9c..47d2ec2 100644
--- a/src/listener.ts
+++ b/src/listener.ts
@@ -1,14 +1,14 @@
 import {CALL_TYPE, RESPONSE_TYPE} from "./constants";
-import {RPCRequest, WindowLike} from "./types";
+import {MessageTarget, RPCRequest, WindowLike} from "./types";
 
 export default class Listener {
-    public fallbackSource: WindowLike; // Only for debugging
+    public fallbackSource: MessageTarget; // Only for testing
 
     constructor(private readonly methods: {[fn: string]: (...args: any[]) => any}) {}
 
     private sendResult(event: MessageEvent<RPCRequest>, result: any): void {
         const {channel, id} = event.data;
-        const source: WindowLike = (event.source as Window) || this.fallbackSource;
+        const source: MessageTarget = (event.source as MessageTarget) || this.fallbackSource;
         const targetOrigin = event.origin && event.origin !== "null" ? event.origin : "*";
 
         Promise.resolve(result).then(r => {
@@ -18,7 +18,7 @@ export default class Listener {
 
     private sendError(event: MessageEvent<RPCRequest>, error: any): void {
         const {channel, id} = event.data;
-        const source: WindowLike = (event.source as Window) || this.fallbackSource;
+        const source: MessageTarget = (event.source as MessageTarget) || this.fallbackSource;
         const targetOrigin = event.origin && event.origin !== "null" ? event.origin : "*";
 
         source.postMessage({'@rpc': RESPONSE_TYPE, channel, id, error}, targetOrigin);
diff --git a/src/sender.ts b/src/sender.ts
index a3a9e3b..fe5e002 100644
--- a/src/sender.ts
+++ b/src/sender.ts
@@ -1,5 +1,5 @@
 import {CALL_TYPE, RESPONSE_TYPE} from "./constants";
-import {RPCResponse, WindowLike} from "./types";
+import {MessageTarget, RPCResponse, WindowLike} from "./types";
 
 interface Options {
     timeout?: number
@@ -7,16 +7,23 @@ interface Options {
 
 let currentChannelId = 1;
 
+export class Cancelled extends Error {}
+
 export function connect<T extends {[name: string]: (...args: any) => Promise<any>}>(
     parent: WindowLike,
-    child: WindowLike,
+    child: MessageTarget,
     targetOrigin: string,
     options: Options = {},
 ): T {
-    let currentId = 1;
+    let currentId = 0;
     const promises = new Map<number, {resolve: (v: any) => void; reject: (reason?: any) => void, timeoutId?: number}>();
     const channel = currentChannelId++;
 
+    function newId() {
+        if (currentId < 0) throw new Error("RPC no longer usable. Handler is removed");
+        return ++currentId;
+    }
+
     function call(id: number, fn: string, args: Array<any>): void {
         child.postMessage({'@rpc': CALL_TYPE, channel, id, fn, args}, targetOrigin);
     }
@@ -34,6 +41,18 @@ export function connect<T extends {[name: string]: (...args: any) => Promise<any
         });
     }
 
+    function destroy() {
+        parent.removeEventListener("message", handler);
+
+        for (const {reject, timeoutId} of promises.values()) {
+            reject(new Cancelled("Event handler removed"));
+            parent.clearTimeout(timeoutId);
+        }
+        promises.clear();
+
+        currentId = -1;
+    }
+
     const handler = (event: MessageEvent<RPCResponse>) => {
         if (
             (targetOrigin !== "*" && event.origin !== targetOrigin) ||
@@ -60,7 +79,7 @@ export function connect<T extends {[name: string]: (...args: any) => Promise<any
     return new Proxy({} as T, {
         get: function get(_, name: string) {
             return function wrapper() {
-                const id = currentId++;
+                const id = newId();
                 const args = Array.prototype.slice.call(arguments);
 
                 const promise = waitFor(id, name);
@@ -71,7 +90,7 @@ export function connect<T extends {[name: string]: (...args: any) => Promise<any
         },
         deleteProperty(_: T, prop: string | symbol): boolean {
             if (prop === 'handler') {
-                parent.removeEventListener("message", handler);
+                destroy();
                 return true;
             }
             return false;
diff --git a/src/types.d.ts b/src/types.d.ts
index 40a98f7..21d51da 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -18,3 +18,5 @@ export type WindowLike = Pick<
     Window,
     "addEventListener" | "removeEventListener" | "postMessage" | "setTimeout" | "clearTimeout"
 >
+
+export type MessageTarget = Pick<Window, "postMessage">
diff --git a/test/index.spec.ts b/test/index.spec.ts
index 45f62d1..10f5c63 100644
--- a/test/index.spec.ts
+++ b/test/index.spec.ts
@@ -66,7 +66,6 @@ describe("simple-iframe-rpc", () => {
 
     it("gives a timeout when there's no response", async () => {
         const child = new JSDOM('').window; // child without listener
-        const parent = new JSDOM('').window;
         const rpc = connect<MathRPC>(parent, child, "*", {timeout: 100});
 
         try {
@@ -77,19 +76,31 @@ describe("simple-iframe-rpc", () => {
         }
     });
 
-    it("will return the handler to remove the event listener A", async () => {
-        const rpc = connect<MathRPC>(parent, child, "*", {timeout: 100});
+    it("will remove the event handler", async () => {
+        const rpc = connect<MathRPC>(parent, child, "*");
 
         assert.equal(await rpc.add(2, 3), 5);
 
         delete (rpc as any).handler;
 
-        // Should time out because there's no handler.
         try {
             await rpc.add(1, 2);
             assert.fail("No error was thrown");
         } catch (e) {
-            assert.equal(e.message, 'No response for RCP call \'add\'');
+            assert.equal(e.message, 'RPC no longer usable. Handler is removed');
         }
     });
+
+    it("will cancel when removing the event handler", async () => {
+        const child = new JSDOM('').window; // child without listener
+        const rpc = connect<MathRPC>(parent, child, "*", {timeout: 10000});
+
+        const promise = rpc.add(2, 3)
+            .then(() => assert.fail("No error was thrown"))
+            .catch(reason => assert.equal(reason.message, "Event handler removed"))
+
+        delete (rpc as any).handler;
+
+        await promise;
+    });
 });