diff --git a/test/parallel/test-worker-exit-code.js b/test/parallel/test-worker-exit-code.js
index bb47e1cece7a62..b621389b49ca6b 100644
--- a/test/parallel/test-worker-exit-code.js
+++ b/test/parallel/test-worker-exit-code.js
@@ -7,9 +7,11 @@ const common = require('../common');
 
 const assert = require('assert');
 const worker = require('worker_threads');
-const { Worker, isMainThread, parentPort } = worker;
+const { Worker, parentPort } = worker;
 
-if (isMainThread) {
+// Do not use isMainThread so that this test itself can be run inside a Worker.
+if (!process.env.HAS_STARTED_WORKER) {
+  process.env.HAS_STARTED_WORKER = 1;
   parent();
 } else {
   if (!parentPort) {
diff --git a/test/parallel/test-worker-onmessage.js b/test/parallel/test-worker-onmessage.js
index 895536c15038be..2ae3d90f852ba9 100644
--- a/test/parallel/test-worker-onmessage.js
+++ b/test/parallel/test-worker-onmessage.js
@@ -2,9 +2,11 @@
 'use strict';
 const common = require('../common');
 const assert = require('assert');
-const { Worker, isMainThread, parentPort } = require('worker_threads');
+const { Worker, parentPort } = require('worker_threads');
 
-if (isMainThread) {
+// Do not use isMainThread so that this test itself can be run inside a Worker.
+if (!process.env.HAS_STARTED_WORKER) {
+  process.env.HAS_STARTED_WORKER = 1;
   const w = new Worker(__filename);
   w.on('message', common.mustCall((message) => {
     assert.strictEqual(message, 4);