---
title: "Must not access ServerResponse after `getServerSideProps` resolves"
url: "https://nextjs.org/docs/messages/gssp-no-mutating-res"
docs_index: /docs/llms.txt
---



## Why This Error Occurred

`getServerSideProps()` surfaces a `ServerResponse` object through the `res` property of its `context` arg. This object is not intended to be accessed or changed after `getServerSideProps()` resolves.

This is because the framework tries to optimize when items like headers or status codes are flushed to the browser. If they are changed after `getServerSideProps()` completes, we can't guarantee that the changes will work.

For this reason, accessing the object after this time is disallowed.

## Possible Ways to Fix It

You can fix this error by moving any access of the `res` object into `getServerSideProps()` itself or any functions that run before `getServerSideProps()` returns.

If you’re using a custom server and running into this problem due to session proxy like `next-session` or `express-session`, try installing the proxy in the server instead of `getServerSideProps()`.

## Useful Links

- [Data Fetching Docs](/docs/pages/building-your-application/data-fetching)