diff --git a/test/parallel/test-worker-message-not-serializable.js b/test/parallel/test-worker-message-not-serializable.js
index 875cc1d58a148a..3753c7de6cbdf9 100644
--- a/test/parallel/test-worker-message-not-serializable.js
+++ b/test/parallel/test-worker-message-not-serializable.js
@@ -6,20 +6,19 @@
 // expected.
 
 const common = require('../common');
-common.skipIfWorker();
 
 const assert = require('assert');
 
-const { Worker, isMainThread } = require('worker_threads');
-if (isMainThread) {
-  const worker = new Worker(__filename);
-  worker.on('error', common.mustCall((e) => {
-    assert.strictEqual(e.code, 'ERR_WORKER_UNSERIALIZABLE_ERROR');
-  }));
-} else {
+const { Worker } = require('worker_threads');
+
+const worker = new Worker(`
   const { internalBinding } = require('internal/test/binding');
   const { getEnvMessagePort } = internalBinding('worker');
   const { messageTypes } = require('internal/worker/io');
   const messagePort = getEnvMessagePort();
   messagePort.postMessage({ type: messageTypes.COULD_NOT_SERIALIZE_ERROR });
-}
+`, { eval: true });
+
+worker.on('error', common.mustCall((e) => {
+  assert.strictEqual(e.code, 'ERR_WORKER_UNSERIALIZABLE_ERROR');
+}));
diff --git a/test/parallel/test-worker-message-type-unknown.js b/test/parallel/test-worker-message-type-unknown.js
new file mode 100644
index 00000000000000..32f6c2a32bd6b4
--- /dev/null
+++ b/test/parallel/test-worker-message-type-unknown.js
@@ -0,0 +1,25 @@
+'use strict';
+
+// Check that main thread handles an unknown message type from a worker thread
+// as expected.
+
+require('../common');
+
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+
+const { Worker } = require('worker_threads');
+if (process.argv[2] !== 'spawned') {
+  const result = spawnSync(process.execPath,
+                           [ '--expose-internals', __filename, 'spawned'],
+                           { encoding: 'utf8' });
+  assert.ok(result.stderr.includes('Unknown worker message type FHQWHGADS'),
+            `Expected error not found in: ${result.stderr}`);
+} else {
+  new Worker(`
+    const { internalBinding } = require('internal/test/binding');
+    const { getEnvMessagePort } = internalBinding('worker');
+    const messagePort = getEnvMessagePort();
+    messagePort.postMessage({ type: 'FHQWHGADS' });
+    `, { eval: true });
+}