Error when using Express 5 as custom server: "Cannot set property query of #<IncomingMessage> which has only a getter"

[TrevorBurnham]

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/ws2m7y

To Reproduce

1. Start the custom server in development mode with node server.mjs
2. Navigate to /api/hello in the browser

The response will fail and the console will show this error:

 ⨯ [TypeError: Cannot set property query of #<IncomingMessage> which has only a getter] {
  page: '/api/hello'
}

Current vs. Expected behavior

I had no trouble using Express 4 as a custom server in front of Next.js. But when I tried to upgrade to Express 5, I started seeing this error when trying to access any API endpoint in the Pages Router. Pages still load fine.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Sun Aug  6 20:05:33 UTC 2023
  Available memory (MB): 4242
  Available CPU cores: 2
Binaries:
  Node: 20.12.0
  npm: 10.5.0
  Yarn: 1.22.19
  pnpm: 8.15.6
Relevant Packages:
  next: 15.2.0 // There is a newer version (15.3.2) available, upgrade recommended! 
  eslint-config-next: 15.2.0
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Not sure

Which stage(s) are affected? (Select all that apply)

next dev (local)

Additional context

I was able to reproduce the same error in 14.2.26. My guess would be that Next.js has always had a compatibility issue with Express 5, though if that's the case then I'm surprised I haven't seen more reports of this issue.

[rachel-bernard]

I have exactly this issue. I was also surprised why I haven't seen it reported anywhere.
I thought once I was able to upgrade to next v15 it might resolve but it has not.

My API routes are not getting hit and I see the error TypeError: Cannot set property query of #<IncomingMessage> which has only a getter
I am not attempting to set the value of query or req.query anywhere.

Everything else is working fine in my application, the only issue I have is when I try to call an API route.

[arishoham]

Getting the same issue, looks to be caused by this line

next.js/packages/next/src/server/api-utils/node/api-resolver.ts

Line 356 in 8370d49

apiReq.query = query

[AlfonsZunderSystems]

"next": "^15.1.7",

The same problem . No "req.query =". when i use fetch post to get data to push in a datatable--> TypeError: Cannot set property query of # which has only a getter

My error is in compiling time.

my code

export default async function handler(req, res) {
console.log('hello!');
}

S.O.S

any idea?

i use custom-server.

[marceljager9]

same issue here

I get error 500 when calling api route

export default function handler(
  req: NextApiRequest,
  res: NextApiResponse<ResponseData>
) {
  res.status(200).json({ message: 'Hello from Next.js!' })
}

next: 15.3.2
express: 5.1.0

custom server