diff --git a/vite.config.ts b/vite.config.ts
index ac5243e..e6faab7 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -17,5 +17,6 @@ export default defineConfig({
     environment: 'happy-dom',
     setupFiles: '.vitest/setup',
     include: ['**/*.test.{ts,tsx}']
-  }
+  },
+  worker: { format: 'es' }
 });