diff --git a/libs/wingsdk/src/shared/sandbox.ts b/libs/wingsdk/src/shared/sandbox.ts
index f8f2739a5a8..a3c0b866c71 100644
--- a/libs/wingsdk/src/shared/sandbox.ts
+++ b/libs/wingsdk/src/shared/sandbox.ts
@@ -37,7 +37,7 @@ export class Sandbox {
     entrypoint: string,
     log?: (message: string) => void
   ): Promise<Bundle> {
-    let contents = (await readFile(entrypoint)).toString();
+    let contents = await readFile(entrypoint, "utf-8");
 
     // log a warning if contents includes __dirname or __filename
     if (contents.includes("__dirname") || contents.includes("__filename")) {
@@ -48,9 +48,7 @@ export class Sandbox {
 
     // wrap contents with a shim that handles the communication with the parent process
     // we insert this shim before bundling to ensure source maps are generated correctly
-    contents = `
-"use strict";
-${contents}
+    contents += `
 process.on("message", async (message) => {
   const { fn, args } = message;
   try {