diff --git a/node_modules/@jspm/core/nodelibs/browser/worker_threads.js b/node_modules/@jspm/core/nodelibs/browser/worker_threads.js
index 23f0041..ba0c53f 100644
--- a/node_modules/@jspm/core/nodelibs/browser/worker_threads.js
+++ b/node_modules/@jspm/core/nodelibs/browser/worker_threads.js
@@ -93,9 +93,9 @@ if (!isMainThread) {
 
   parentPort.emit = () => notImplemented();
   parentPort.removeAllListeners = () => notImplemented();
-
+(async () => {
   ([{ threadId, workerData, environmentData }] = await once(parentPort, 'message'));
-
+})();
   // alias
   parentPort.addEventListener('offline', () => parentPort.emit('close'));
 }