diff --git a/lib/npm/browser.ts b/lib/npm/browser.ts
index 0196f3329bb..8dbdc24b1ef 100644
--- a/lib/npm/browser.ts
+++ b/lib/npm/browser.ts
@@ -3,8 +3,8 @@ import * as common from "../shared/common"
 import * as ourselves from "./browser"
 
 declare const ESBUILD_VERSION: string;
+declare let WEB_WORKER_SOURCE_CODE: string
 declare let WEB_WORKER_FUNCTION: (postMessage: (data: Uint8Array) => void) => (event: { data: Uint8Array | ArrayBuffer }) => void
-let webWorkerFunction = WEB_WORKER_FUNCTION
 
 export let version = ESBUILD_VERSION;
 
@@ -83,11 +83,11 @@ const startRunningService = async (wasmURL: string, useWorker: boolean): Promise
 
   if (useWorker) {
     // Run esbuild off the main thread
-    let blob = new Blob([`onmessage=(${webWorkerFunction})(postMessage)`], { type: 'text/javascript' })
+    let blob = new Blob([`onmessage=${WEB_WORKER_SOURCE_CODE}(postMessage)`], { type: 'text/javascript' })
     worker = new Worker(URL.createObjectURL(blob))
   } else {
     // Run esbuild on the main thread
-    let onmessage = webWorkerFunction((data: Uint8Array) => worker.onmessage!({ data }))
+    let onmessage = WEB_WORKER_FUNCTION((data: Uint8Array) => worker.onmessage!({ data }))
     worker = {
       onmessage: null,
       postMessage: data => onmessage({ data }),
diff --git a/scripts/esbuild.js b/scripts/esbuild.js
index 56e8650b49c..e6287d194e3 100644
--- a/scripts/esbuild.js
+++ b/scripts/esbuild.js
@@ -188,8 +188,8 @@ exports.buildWasmLib = async (esbuildPath) => {
       const firstNonComment = commentLines.findIndex(line => !line.startsWith('//'))
       const commentPrefix = '\n' + commentLines.slice(0, firstNonComment).join('\n') + '\n'
       wasmWorkerCode[format] = minify
-        ? `postMessage=>{${commentPrefix}${wasmExecAndWorker}}`
-        : `(postMessage) => {${(commentPrefix + wasmExecAndWorker).replace(/\n/g, '\n  ')}\n}`
+        ? `(postMessage=>{${commentPrefix}${wasmExecAndWorker}})`
+        : `((postMessage) => {${(commentPrefix + wasmExecAndWorker).replace(/\n/g, '\n      ')}\n    })`
     }
 
     // Generate "npm/esbuild-wasm/lib/browser.*"
@@ -201,6 +201,7 @@ exports.buildWasmLib = async (esbuildPath) => {
       '--target=' + umdBrowserTarget,
       '--format=cjs',
       '--define:ESBUILD_VERSION=' + JSON.stringify(version),
+      '--define:WEB_WORKER_SOURCE_CODE=' + JSON.stringify(wasmWorkerCode.umd),
       '--banner:js=' + umdPrefix,
       '--footer:js=' + umdSuffix,
       '--log-level=warning',
@@ -214,6 +215,7 @@ exports.buildWasmLib = async (esbuildPath) => {
       '--target=' + esmBrowserTarget,
       '--format=esm',
       '--define:ESBUILD_VERSION=' + JSON.stringify(version),
+      '--define:WEB_WORKER_SOURCE_CODE=' + JSON.stringify(wasmWorkerCode.esm),
       '--log-level=warning',
     ].concat(minifyFlags), { cwd: repoDir }).toString().replace('WEB_WORKER_FUNCTION', wasmWorkerCode.esm)
     fs.writeFileSync(path.join(esmDir, minify ? 'browser.min.js' : 'browser.js'), browserESM)