vercel · anthony-schanen · Mar 4, 2026 · Mar 11, 2026 · Apr 22, 2026 · Apr 22, 2026
diff --git a/packages/next/src/server/lib/patch-fetch.ts b/packages/next/src/server/lib/patch-fetch.ts
@@ -803,15 +803,27 @@ export function createPatchedFetcher(
 
           if (isRequestInput) {
             const reqInput: Request = input as any
-            const reqOptions: RequestInit = {
-              body: (reqInput as any)._ogBody || reqInput.body,
-            }
+            const reqOptions: RequestInit = {}
 
             for (const field of requestInputFields) {
               // @ts-expect-error custom fields
               reqOptions[field] = reqInput[field]
             }
-            input = new Request(reqInput.url, reqOptions)
+
+            const ogBody = (reqInput as any)._ogBody
+            if (ogBody !== undefined) {
+              reqOptions.body = ogBody
+              input = new Request(reqInput.url, reqOptions)
+            } else {
+              // When _ogBody is absent, the body stream hasn't been consumed.
+              // Pass the original Request object instead of reqInput.url to
+              // preserve the internal body source, which Node 24.14+ (undici)
+              // requires to be non-null for requests with a body.
+              if (isStale) {
+                reqOptions.signal = null
+              }
+              input = new Request(reqInput, reqOptions)
+            }
           } else if (init) {
             const { _ogBody, body, signal, ...otherInput } =
               init as RequestInit & { _ogBody?: any }

diff --git a/test/e2e/app-dir/patch-fetch-request-body/app/api/test-post/route.ts b/test/e2e/app-dir/patch-fetch-request-body/app/api/test-post/route.ts
@@ -0,0 +1,16 @@
+import { NextResponse } from 'next/server'
+
+export async function POST() {
+  const req = new Request(
+    `http://localhost:${process.env.EXTERNAL_SERVER_PORT}/post`,
+    {
+      method: 'POST',
+      body: JSON.stringify({ key: 'value' }),
+      headers: { 'Content-Type': 'application/json' },
+    }
+  )
+
+  const res = await fetch(req)
+  const data = await res.json()
+  return NextResponse.json({ status: res.status, data })
+}
diff --git a/test/e2e/app-dir/patch-fetch-request-body/app/layout.tsx b/test/e2e/app-dir/patch-fetch-request-body/app/layout.tsx
@@ -0,0 +1,8 @@
+import { ReactNode } from 'react'
+export default function Root({ children }: { children: ReactNode }) {
+  return (
+    <html>
+      <body>{children}</body>
+    </html>
+  )
+}
diff --git a/test/e2e/app-dir/patch-fetch-request-body/app/page.tsx b/test/e2e/app-dir/patch-fetch-request-body/app/page.tsx
@@ -0,0 +1,3 @@
+export default function Page() {
+  return <p>hello world</p>
+}
diff --git a/test/e2e/app-dir/patch-fetch-request-body/next.config.js b/test/e2e/app-dir/patch-fetch-request-body/next.config.js
@@ -0,0 +1,6 @@
+/**
+ * @type {import('next').NextConfig}
+ */
+const nextConfig = {}
+
+module.exports = nextConfig
diff --git a/test/e2e/app-dir/patch-fetch-request-body/patch-fetch-request-body.test.ts b/test/e2e/app-dir/patch-fetch-request-body/patch-fetch-request-body.test.ts
@@ -0,0 +1,53 @@
+import { nextTestSetup } from 'e2e-utils'
+import { findPort } from 'next-test-utils'
+import http from 'http'
+
+describe('patch-fetch-request-body', () => {
+  let externalServerPort: number
+  let externalServer: http.Server
+
+  const { next, skipped } = nextTestSetup({
+    files: __dirname,
+    skipStart: true,
+    skipDeployment: true,
+  })
+
+  if (skipped) {
+    return
+  }
+
+  beforeAll(async () => {
+    externalServerPort = await findPort()
+
+    externalServer = http.createServer((req, res) => {
+      req.resume()
+      req.on('end', () => {
+        res.writeHead(401, { 'Content-Type': 'application/json' })
+        res.end(JSON.stringify({ status: 401 }))
+      })
+    })
+
+    await new Promise<void>((resolve, reject) => {
+      externalServer.listen(externalServerPort, () => resolve())
+      externalServer.once('error', reject)
+    })
+
+    next.env.EXTERNAL_SERVER_PORT = String(externalServerPort)
+    await next.start()
+  })
+
+  afterAll(() => {
+    externalServer?.close()
+  })
+
+  // On Node 24.14+, patch-fetch previously reconstructed the Request using
+  // reqInput.url which lost the internal body source. undici then threw
+  // "TypeError: expected non-null body source" when sending the request.
+  it('should preserve Request body source for uncached POST requests', async () => {
+    const res = await next.fetch('/api/test-post', { method: 'POST' })
+    expect(res.status).toBe(200)
+
+    const json = await res.json()
+    expect(json.status).toBe(401)
+  })
+})