diff --git a/test/parallel/test-worker-message-not-serializable.js b/test/parallel/test-worker-message-not-serializable.js
new file mode 100644
index 00000000000000..3753c7de6cbdf9
--- /dev/null
+++ b/test/parallel/test-worker-message-not-serializable.js
@@ -0,0 +1,24 @@
+'use strict';
+
+// Flags: --expose-internals
+
+// Check that main thread handles unserializable errors in a worker thread as
+// expected.
+
+const common = require('../common');
+
+const assert = require('assert');
+
+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 });
+}