diff --git a/lib/internal/process/worker_thread_only.js b/lib/internal/process/worker_thread_only.js
index a9332fb4277363..d26159ab451c97 100644
--- a/lib/internal/process/worker_thread_only.js
+++ b/lib/internal/process/worker_thread_only.js
@@ -7,18 +7,21 @@ const {
   threadId
 } = internalBinding('worker');
 
-const debug = require('util').debuglog('worker');
-
 const {
+  messageTypes,
+  kStdioWantsMoreDataCallback,
   kWaitingStreams,
   ReadableWorkerStdio,
   WritableWorkerStdio
 } = require('internal/worker/io');
 
-const {
-  createMessageHandler,
-  createWorkerFatalExeception
-} = require('internal/worker');
+let debuglog;
+function debug(...args) {
+  if (!debuglog) {
+    debuglog = require('util').debuglog('worker');
+  }
+  return debuglog(...args);
+}
 
 const workerStdio = {};
 
@@ -36,12 +39,90 @@ function initializeWorkerStdio() {
   };
 }
 
+function createMessageHandler(port) {
+  const publicWorker = require('worker_threads');
+
+  return function(message) {
+    if (message.type === messageTypes.LOAD_SCRIPT) {
+      const { filename, doEval, workerData, publicPort, hasStdin } = message;
+      publicWorker.parentPort = publicPort;
+      publicWorker.workerData = workerData;
+
+      if (!hasStdin)
+        workerStdio.stdin.push(null);
+
+      debug(`[${threadId}] starts worker script ${filename} ` +
+            `(eval = ${eval}) at cwd = ${process.cwd()}`);
+      port.unref();
+      port.postMessage({ type: messageTypes.UP_AND_RUNNING });
+      if (doEval) {
+        const { evalScript } = require('internal/process/execution');
+        evalScript('[worker eval]', filename);
+      } else {
+        process.argv[1] = filename; // script filename
+        require('module').runMain();
+      }
+      return;
+    } else if (message.type === messageTypes.STDIO_PAYLOAD) {
+      const { stream, chunk, encoding } = message;
+      workerStdio[stream].push(chunk, encoding);
+      return;
+    } else if (message.type === messageTypes.STDIO_WANTS_MORE_DATA) {
+      const { stream } = message;
+      workerStdio[stream][kStdioWantsMoreDataCallback]();
+      return;
+    }
+
+    require('assert').fail(`Unknown worker message type ${message.type}`);
+  };
+}
+
+// XXX(joyeecheung): this has to be returned as an anonymous function
+// wrapped in a closure, see the comment of the original
+// process._fatalException in lib/internal/process/execution.js
+function createWorkerFatalExeception(port) {
+  const {
+    fatalException: originalFatalException
+  } = require('internal/process/execution');
+
+  return (error) => {
+    debug(`[${threadId}] gets fatal exception`);
+    let caught = false;
+    try {
+      caught = originalFatalException.call(this, error);
+    } catch (e) {
+      error = e;
+    }
+    debug(`[${threadId}] fatal exception caught = ${caught}`);
+
+    if (!caught) {
+      let serialized;
+      try {
+        const { serializeError } = require('internal/error-serdes');
+        serialized = serializeError(error);
+      } catch {}
+      debug(`[${threadId}] fatal exception serialized = ${!!serialized}`);
+      if (serialized)
+        port.postMessage({
+          type: messageTypes.ERROR_MESSAGE,
+          error: serialized
+        });
+      else
+        port.postMessage({ type: messageTypes.COULD_NOT_SERIALIZE_ERROR });
+
+      const { clearAsyncIdStack } = require('internal/async_hooks');
+      clearAsyncIdStack();
+
+      process.exit();
+    }
+  };
+}
+
 function setup() {
   debug(`[${threadId}] is setting up worker child environment`);
 
   const port = getEnvMessagePort();
-  const publicWorker = require('worker_threads');
-  port.on('message', createMessageHandler(publicWorker, port, workerStdio));
+  port.on('message', createMessageHandler(port));
   port.start();
 
   return {
diff --git a/lib/internal/worker.js b/lib/internal/worker.js
index c4393d0459cf7e..2e1568a73822b9 100644
--- a/lib/internal/worker.js
+++ b/lib/internal/worker.js
@@ -10,7 +10,6 @@ const {
   ERR_WORKER_UNSUPPORTED_EXTENSION,
 } = require('internal/errors').codes;
 const { validateString } = require('internal/validators');
-const { clearAsyncIdStack } = require('internal/async_hooks');
 
 const {
   drainMessagePort,
@@ -24,7 +23,7 @@ const {
   ReadableWorkerStdio,
   WritableWorkerStdio,
 } = require('internal/worker/io');
-const { serializeError, deserializeError } = require('internal/error-serdes');
+const { deserializeError } = require('internal/error-serdes');
 const { pathToFileURL } = require('url');
 
 const {
@@ -219,77 +218,6 @@ class Worker extends EventEmitter {
   }
 }
 
-function createMessageHandler(publicWorker, port, workerStdio) {
-  return function(message) {
-    if (message.type === messageTypes.LOAD_SCRIPT) {
-      const { filename, doEval, workerData, publicPort, hasStdin } = message;
-      publicWorker.parentPort = publicPort;
-      publicWorker.workerData = workerData;
-
-      if (!hasStdin)
-        workerStdio.stdin.push(null);
-
-      debug(`[${threadId}] starts worker script ${filename} ` +
-            `(eval = ${eval}) at cwd = ${process.cwd()}`);
-      port.unref();
-      port.postMessage({ type: messageTypes.UP_AND_RUNNING });
-      if (doEval) {
-        const { evalScript } = require('internal/process/execution');
-        evalScript('[worker eval]', filename);
-      } else {
-        process.argv[1] = filename; // script filename
-        require('module').runMain();
-      }
-      return;
-    } else if (message.type === messageTypes.STDIO_PAYLOAD) {
-      const { stream, chunk, encoding } = message;
-      workerStdio[stream].push(chunk, encoding);
-      return;
-    } else if (message.type === messageTypes.STDIO_WANTS_MORE_DATA) {
-      const { stream } = message;
-      workerStdio[stream][kStdioWantsMoreDataCallback]();
-      return;
-    }
-
-    assert.fail(`Unknown worker message type ${message.type}`);
-  };
-}
-
-function createWorkerFatalExeception(port) {
-  const {
-    fatalException: originalFatalException
-  } = require('internal/process/execution');
-
-  return function(error) {
-    debug(`[${threadId}] gets fatal exception`);
-    let caught = false;
-    try {
-      caught = originalFatalException.call(this, error);
-    } catch (e) {
-      error = e;
-    }
-    debug(`[${threadId}] fatal exception caught = ${caught}`);
-
-    if (!caught) {
-      let serialized;
-      try {
-        serialized = serializeError(error);
-      } catch {}
-      debug(`[${threadId}] fatal exception serialized = ${!!serialized}`);
-      if (serialized)
-        port.postMessage({
-          type: messageTypes.ERROR_MESSAGE,
-          error: serialized
-        });
-      else
-        port.postMessage({ type: messageTypes.COULD_NOT_SERIALIZE_ERROR });
-      clearAsyncIdStack();
-
-      process.exit();
-    }
-  };
-}
-
 function pipeWithoutWarning(source, dest) {
   const sourceMaxListeners = source._maxListeners;
   const destMaxListeners = dest._maxListeners;
@@ -303,8 +231,6 @@ function pipeWithoutWarning(source, dest) {
 }
 
 module.exports = {
-  createMessageHandler,
-  createWorkerFatalExeception,
   threadId,
   Worker,
   isMainThread