diff --git a/cli/tests/workers/http_worker.js b/cli/tests/workers/http_worker.js
index ee2e5397ec..6a3b49b56a 100644
--- a/cli/tests/workers/http_worker.js
+++ b/cli/tests/workers/http_worker.js
@@ -1,5 +1,6 @@
 // Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
 const listener = Deno.listen({ hostname: "127.0.0.1", port: 4500 });
+postMessage("ready");
 for await (const conn of listener) {
   (async () => {
     const requests = Deno.serveHttp(conn);
diff --git a/cli/tests/workers/test.ts b/cli/tests/workers/test.ts
index 72b87e3984..c3ccebfbb9 100644
--- a/cli/tests/workers/test.ts
+++ b/cli/tests/workers/test.ts
@@ -701,6 +701,7 @@ Deno.test({
 Deno.test({
   name: "Worker with native HTTP",
   fn: async function () {
+    const result = deferred();
     const worker = new Worker(
       new URL(
         "./http_worker.js",
@@ -714,6 +715,10 @@ Deno.test({
         },
       },
     );
+    worker.onmessage = () => {
+      result.resolve();
+    };
+    await result;
 
     assert(worker);
     const response = await fetch("http://localhost:4500");