5 files changed, 31 insertions, 1 deletions
diff --git a/cli/tests/unit_node/testdata/worker_module/index.js b/cli/tests/unit_node/testdata/worker_module/index.js
new file mode 100644
index 000000000..a3e976b65
--- /dev/null
+++ b/cli/tests/unit_node/testdata/worker_module/index.js
@@ -0,0 +1,3 @@
+import { myFunction } from "./other_file.js";
+
+myFunction().then(() => {});
diff --git a/cli/tests/unit_node/testdata/worker_module/other_file.js b/cli/tests/unit_node/testdata/worker_module/other_file.js
new file mode 100644
index 000000000..41789dfe8
--- /dev/null
+++ b/cli/tests/unit_node/testdata/worker_module/other_file.js
@@ -0,0 +1,3 @@
+export async function myFunction() {
+  await new Promise((resolve) => setTimeout(resolve, 100));
+}
diff --git a/cli/tests/unit_node/testdata/worker_module/package.json b/cli/tests/unit_node/testdata/worker_module/package.json
new file mode 100644
index 000000000..486d2f82b
--- /dev/null
+++ b/cli/tests/unit_node/testdata/worker_module/package.json
@@ -0,0 +1,4 @@
+{
+  "name": "foo",
+  "type": "module"
+}
diff --git a/cli/tests/unit_node/worker_threads_test.ts b/cli/tests/unit_node/worker_threads_test.ts
index f53b1e692..c46df057e 100644
--- a/cli/tests/unit_node/worker_threads_test.ts
+++ b/cli/tests/unit_node/worker_threads_test.ts
@@ -134,6 +134,16 @@ Deno.test({
 });
 
 Deno.test({
+  name: "[worker_threads] worker thread with type module",
+  fn() {
+    const worker = new workerThreads.Worker(
+      new URL("./testdata/worker_module/index.js", import.meta.url),
+    );
+    worker.terminate();
+  },
+});
+
+Deno.test({
   name: "[worker_threads] inheritences",
   async fn() {
     const worker = new workerThreads.Worker(
diff --git a/ext/node/polyfills/worker_threads.ts b/ext/node/polyfills/worker_threads.ts
index 8005506bb..32f9885af 100644
--- a/ext/node/polyfills/worker_threads.ts
+++ b/ext/node/polyfills/worker_threads.ts
@@ -9,6 +9,7 @@ import { MessageChannel, MessagePort } from "ext:deno_web/13_message_port.js";
 
 let environmentData = new Map();
 let threads = 0;
+const { core } = globalThis.__bootstrap;
 
 export interface WorkerOptions {
   // only for typings
@@ -53,7 +54,16 @@ class _Worker extends EventEmitter {
       specifier = `data:text/javascript,${specifier}`;
     } else if (typeof specifier === "string") {
       specifier = resolve(specifier);
-      if (!specifier.toString().endsWith(".mjs")) {
+      let pkg;
+      try {
+        pkg = core.ops.op_require_read_closest_package_json(specifier);
+      } catch (_) {
+        // empty catch block when package json might not be present
+      }
+      if (
+        !(specifier.toString().endsWith(".mjs") ||
+          (pkg && pkg.exists && pkg.typ == "module"))
+      ) {
         const cwdFileUrl = toFileUrl(Deno.cwd());
         specifier =
           `data:text/javascript,(async function() {const { createRequire } = await import("node:module");const require = createRequire("${cwdFileUrl}");require("${specifier}");})();`;