diff --git a/packages/plugin-react-swc/playground/bundled-dev/__tests__/bundled-dev.spec.ts b/packages/plugin-react-swc/playground/bundled-dev/__tests__/bundled-dev.spec.ts
new file mode 100644
index 000000000..6fb03381c
--- /dev/null
+++ b/packages/plugin-react-swc/playground/bundled-dev/__tests__/bundled-dev.spec.ts
@@ -0,0 +1,16 @@
+import { expect, test } from '@playwright/test'
+import { setupDevServer } from '../../utils.ts'
+
+test('bundledDev mode does not throw config.server error', async ({ page }) => {
+  // The key verification: the dev server should start successfully
+  // without the "Cannot read properties of undefined (reading 'config')" error
+  // that the bug report (#1271) describes.
+  const { testUrl, server } = await setupDevServer('bundled-dev')
+
+  // Verify the server responds to requests (no crash)
+  await page.goto(testUrl)
+  const bodyText = await page.textContent('body')
+  expect(bodyText).toBeTruthy()
+
+  await server.close()
+})
diff --git a/packages/plugin-react-swc/playground/bundled-dev/index.html b/packages/plugin-react-swc/playground/bundled-dev/index.html
new file mode 100644
index 000000000..fb1aeef55
--- /dev/null
+++ b/packages/plugin-react-swc/playground/bundled-dev/index.html
@@ -0,0 +1,2 @@
+<div id="app"></div>
+<script type="module" src="./src/main.tsx"></script>
diff --git a/packages/plugin-react-swc/playground/bundled-dev/package.json b/packages/plugin-react-swc/playground/bundled-dev/package.json
new file mode 100644
index 000000000..da71b9337
--- /dev/null
+++ b/packages/plugin-react-swc/playground/bundled-dev/package.json
@@ -0,0 +1,20 @@
+{
+  "name": "playground-bundled-dev",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "debug": "node --inspect-brk vite",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "react": "^19.2.7",
+    "react-dom": "^19.2.7"
+  },
+  "devDependencies": {
+    "@types/react": "^19.2.17",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react-swc": "../../dist"
+  }
+}
diff --git a/packages/plugin-react-swc/playground/bundled-dev/src/App.tsx b/packages/plugin-react-swc/playground/bundled-dev/src/App.tsx
new file mode 100644
index 000000000..7d9c3a262
--- /dev/null
+++ b/packages/plugin-react-swc/playground/bundled-dev/src/App.tsx
@@ -0,0 +1,14 @@
+import { useState } from 'react'
+
+export default function App() {
+  const [count, setCount] = useState(0)
+
+  return (
+    <>
+      <h1>Hello Vite + React</h1>
+      <button id="state-button" onClick={() => setCount((count) => count + 1)}>
+        count is: {count}
+      </button>
+    </>
+  )
+}
diff --git a/packages/plugin-react-swc/playground/bundled-dev/src/main.tsx b/packages/plugin-react-swc/playground/bundled-dev/src/main.tsx
new file mode 100644
index 000000000..1f5976c1d
--- /dev/null
+++ b/packages/plugin-react-swc/playground/bundled-dev/src/main.tsx
@@ -0,0 +1,4 @@
+import ReactDOM from 'react-dom/client'
+import App from './App.tsx'
+
+ReactDOM.createRoot(document.getElementById('app')!).render(<App />)
diff --git a/packages/plugin-react-swc/playground/bundled-dev/tsconfig.json b/packages/plugin-react-swc/playground/bundled-dev/tsconfig.json
new file mode 100644
index 000000000..195fe84e7
--- /dev/null
+++ b/packages/plugin-react-swc/playground/bundled-dev/tsconfig.json
@@ -0,0 +1,23 @@
+{
+  "include": ["src"],
+  "compilerOptions": {
+    "target": "ES2020",
+    "useDefineForClassFields": true,
+    "lib": ["ES2020", "DOM"],
+    "types": ["vite/client"],
+    "module": "ESNext",
+    "skipLibCheck": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "noEmit": true,
+    "jsx": "react-jsx",
+
+    /* Linting */
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noFallthroughCasesInSwitch": true
+  }
+}
diff --git a/packages/plugin-react-swc/playground/bundled-dev/vite.config.ts b/packages/plugin-react-swc/playground/bundled-dev/vite.config.ts
new file mode 100644
index 000000000..6c4b5d2b4
--- /dev/null
+++ b/packages/plugin-react-swc/playground/bundled-dev/vite.config.ts
@@ -0,0 +1,11 @@
+import react from '@vitejs/plugin-react-swc'
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  base: '/bundled-dev/',
+  server: { port: 8910 /* Should be unique */ },
+  experimental: {
+    bundledDev: true,
+  },
+  plugins: [react()],
+})
diff --git a/packages/plugin-react-swc/src/index.ts b/packages/plugin-react-swc/src/index.ts
index 50aee52bc..de0513940 100644
--- a/packages/plugin-react-swc/src/index.ts
+++ b/packages/plugin-react-swc/src/index.ts
@@ -78,6 +78,7 @@ const usingRolldown = 'rolldownVersion' in vite
 
 const react = (_options?: Options): Plugin[] => {
   let hmrDisabled = true
+  let isBundledDev = false
   let viteCacheRoot: string | undefined
   const options = {
     jsxImportSource: _options?.jsxImportSource ?? 'react',
@@ -143,6 +144,9 @@ const react = (_options?: Options): Plugin[] => {
       },
       configResolved(config) {
         viteCacheRoot = config.cacheDir
+        if (config.experimental.bundledDev) {
+          isBundledDev = true
+        }
         hmrDisabled = config.server.hmr === false
         const mdxIndex = config.plugins.findIndex(
           (p) => p.name === '@mdx-js/rollup',
@@ -169,15 +173,25 @@ const react = (_options?: Options): Plugin[] => {
         }
       },
       transformIndexHtml: (_, config) => {
-        if (!hmrDisabled) {
+        if (hmrDisabled) return
+        if (isBundledDev) {
           return [
             {
               tag: 'script',
               attrs: { type: 'module' },
-              children: getPreambleCode(config.server!.config.base),
+              // In bundled dev mode, the src does not go through the middlewares
+              // so we don't need to append the base
+              children: getPreambleCode('/'),
             },
           ]
         }
+        return [
+          {
+            tag: 'script',
+            attrs: { type: 'module' },
+            children: getPreambleCode(config.server!.config.base),
+          },
+        ]
       },
       async transform(code, _id, transformOptions) {
         const id = _id.split('?')[0]
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index ff4a4784f..91d305a9d 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -165,6 +165,25 @@ importers:
         specifier: ../../dist
         version: link:../../dist
 
+  packages/plugin-react-swc/playground/bundled-dev:
+    dependencies:
+      react:
+        specifier: ^19.2.7
+        version: 19.2.7
+      react-dom:
+        specifier: ^19.2.7
+        version: 19.2.7(react@19.2.7)
+    devDependencies:
+      '@types/react':
+        specifier: ^19.2.17
+        version: 19.2.17
+      '@types/react-dom':
+        specifier: ^19.2.3
+        version: 19.2.3(@types/react@19.2.17)
+      '@vitejs/plugin-react-swc':
+        specifier: ../../dist
+        version: link:../../dist
+
   packages/plugin-react-swc/playground/class-components:
     dependencies:
       react: