diff --git a/src/core/index.ts b/src/core/index.ts
index 1cb9396..e0ddfc3 100644
--- a/src/core/index.ts
+++ b/src/core/index.ts
@@ -5,7 +5,7 @@ export function buildWorkerCode(source: string, moduleType: ModuleType)
     let result = `\
 const WORKER_CODE = ${JSON.stringify(source)};
 let WORKER_URL = null;
-class WorkerInstance extends Worker
+class WorkerInstance
 {
     constructor()
     {
@@ -13,7 +13,7 @@ class WorkerInstance extends Worker
         {
             WORKER_URL = URL.createObjectURL(new Blob([WORKER_CODE], { type: 'application/javascript' }));
         }
-        super(WORKER_URL);
+        this.worker = new Worker(WORKER_URL);
     }
 }
 WorkerInstance.revokeObjectURL = function revokeObjectURL()
diff --git a/test/JestTransform.tests.ts b/test/JestTransform.tests.ts
index 2511cb4..d210701 100644
--- a/test/JestTransform.tests.ts
+++ b/test/JestTransform.tests.ts
@@ -7,13 +7,13 @@ describe('Test', () =>
         {
             const worker = new AdderWorker();
 
-            worker.onmessage = (event) =>
+            worker.worker.onmessage = (event) =>
             {
                 expect(event.data).toBe(2);
                 resolve();
             };
 
-            worker.postMessage({ a: 1, b: 1 });
+            worker.worker.postMessage({ a: 1, b: 1 });
         })
     );
 });
diff --git a/test/global.d.ts b/test/global.d.ts
index 4149edb..6a3efb1 100644
--- a/test/global.d.ts
+++ b/test/global.d.ts
@@ -1,7 +1,9 @@
 declare module '*.worker.ts'
 {
-    class WorkerInstance extends Worker
+    class WorkerInstance
     {
+        public worker: Worker;
+
         constructor();
 
         static revokeObjectURL(): void;