diff --git a/packages/vite/src/node/__tests__/plugins/esbuild.spec.ts b/packages/vite/src/node/__tests__/plugins/esbuild.spec.ts
index 7f5e90db5f68fd..22952ca72da04e 100644
--- a/packages/vite/src/node/__tests__/plugins/esbuild.spec.ts
+++ b/packages/vite/src/node/__tests__/plugins/esbuild.spec.ts
@@ -401,10 +401,19 @@ describe('transformWithEsbuild', () => {
 describe('injectEsbuildHelpers', () => {
   test('injects helpers in IIFE format', () => {
     const esbuildCode =
-      'var $=function(){};var MyLib=function(){"use strict";return 42;}'
+      'var $=function(){};var MyLib=(function(){"use strict";return 42;})()'
     const result = injectEsbuildHelpers(esbuildCode, 'iife')
     expect(result).toBe(
-      'var MyLib=function(){"use strict";var $=function(){};return 42;}',
+      'var MyLib=(function(){"use strict";var $=function(){};return 42;})()',
+    )
+  })
+
+  test('injects helpers in IIFE format (pre esbuild 0.25.9)', () => {
+    const esbuildCode =
+      'var $=function(){};var MyLib=function(){"use strict";return 42;}()'
+    const result = injectEsbuildHelpers(esbuildCode, 'iife')
+    expect(result).toBe(
+      'var MyLib=function(){"use strict";var $=function(){};return 42;}()',
     )
   })
 
@@ -419,7 +428,7 @@ describe('injectEsbuildHelpers', () => {
 
   test('handles helpers with special characters', () => {
     const esbuildCode =
-      'var $$=function(){};var MyLib=function(){"use strict";return 42;}'
+      'var $$=function(){};var MyLib=(function(){"use strict";return 42;})()'
     const result = injectEsbuildHelpers(esbuildCode, 'iife')
     expect(result).toContain('"use strict";var $$=function(){};')
   })
diff --git a/packages/vite/src/node/plugins/esbuild.ts b/packages/vite/src/node/plugins/esbuild.ts
index d48d5a738d6230..c47c310d926a3d 100644
--- a/packages/vite/src/node/plugins/esbuild.ts
+++ b/packages/vite/src/node/plugins/esbuild.ts
@@ -29,7 +29,7 @@ const debug = createDebugger('vite:esbuild')
 // IIFE content looks like `var MyLib = function() {`.
 // Spaces are removed and parameters are mangled when minified
 const IIFE_BEGIN_RE =
-  /(?:const|var)\s+\S+\s*=\s*function\([^()]*\)\s*\{\s*"use strict";/
+  /(?:const|var)\s+\S+\s*=\s*\(?function\([^()]*\)\s*\{\s*"use strict";/
 
 const validExtensionRE = /\.\w+$/
 const jsxExtensionsRE = /\.(?:j|t)sx\b/