diff --git a/src/client/dom/cookie.ts b/src/client/dom/cookie.ts
index fd66875..f8eae03 100644
--- a/src/client/dom/cookie.ts
+++ b/src/client/dom/cookie.ts
@@ -1,13 +1,22 @@
+import type { MessageC2W, MessageW2C } from "../../worker";
 import { ScramjetClient } from "../client";
 
 export default function (client: ScramjetClient, self: typeof window) {
-	client.serviceWorker.addEventListener("message", ({ data }) => {
-		if (!("scramjet$type" in data)) return;
+	client.serviceWorker.addEventListener(
+		"message",
+		({ data }: { data: MessageW2C }) => {
+			if (!("scramjet$type" in data)) return;
 
-		if (data.scramjet$type === "cookie") {
-			client.cookieStore.setCookies([data.cookie], new URL(data.url));
+			if (data.scramjet$type === "cookie") {
+				client.cookieStore.setCookies([data.cookie], new URL(data.url));
+				let msg = {
+					scramjet$token: data.scramjet$token,
+					scramjet$type: "cookie",
+				};
+				client.serviceWorker.controller.postMessage(msg);
+			}
 		}
-	});
+	);
 
 	client.Trap("Document.prototype.cookie", {
 		get() {
diff --git a/src/worker/fetch.ts b/src/worker/fetch.ts
index 4c6f09e..c94b1e9 100644
--- a/src/worker/fetch.ts
+++ b/src/worker/fetch.ts
@@ -237,12 +237,16 @@ async function handleResponse(
 
 	const maybeHeaders = responseHeaders["set-cookie"] || [];
 	for (const cookie in maybeHeaders) {
-		if (client)
-			client.postMessage({
+		if (client) {
+			let promise = swtarget.dispatch(client, {
 				scramjet$type: "cookie",
 				cookie,
 				url: url.href,
-			} as MessageW2C);
+			});
+			if (destination != "document" && destination != "iframe") {
+				await promise;
+			}
+		}
 	}
 
 	await cookieStore.setCookies(
diff --git a/src/worker/index.ts b/src/worker/index.ts
index 5d1f37b..5fe17ad 100644
--- a/src/worker/index.ts
+++ b/src/worker/index.ts
@@ -38,6 +38,14 @@ export class ScramjetServiceWorker extends EventTarget {
 		addEventListener("message", async ({ data }: { data: MessageC2W }) => {
 			if (!("scramjet$type" in data)) return;
 
+			if ("scramjet$token" in data) {
+				// (ack message)
+				const cb = this.syncPool[data.scramjet$token];
+				delete this.syncPool[data.scramjet$token];
+				cb(data);
+				return;
+			}
+
 			if (data.scramjet$type === "registerServiceWorker") {
 				this.serviceWorkers.push(new FakeServiceWorker(data.port, data.origin));
 
@@ -58,6 +66,17 @@ export class ScramjetServiceWorker extends EventTarget {
 		});
 	}
 
+	async dispatch(client: Client, data: MessageW2C): Promise<MessageC2W> {
+		let token = this.synctoken++;
+		let cb: (val: MessageC2W) => void;
+		let promise: Promise<MessageC2W> = new Promise((r) => (cb = r));
+		this.syncPool[token] = cb;
+		data.scramjet$token = token;
+
+		client.postMessage(data);
+		return await promise;
+	}
+
 	async loadConfig() {
 		if (this.config) return;
 
@@ -124,7 +143,7 @@ type ConfigMessage = {
 
 type MessageCommon = {
 	scramjet$type: string;
-	scramjet$token: number;
+	scramjet$token?: number;
 };
 
 type MessageTypeC2W =