---
title: Missing webpack config
url: "https://nextjs.org/docs/messages/undefined-webpack-config"
docs_index: /docs/llms.txt
---



## Why This Error Occurred

The value returned from the custom `webpack` function in your `next.config.js` was undefined. This can occur from the initial config value not being returned.

## Possible Ways to Fix It

Make sure to return the `webpack` config from your custom `webpack` function in your `next.config.js`

```js filename="next.config.js"
module.exports = {
  webpack: (config, { buildId, dev, isServer, defaultLoaders, webpack }) => {
    // Note: we provide webpack above so you should not `require` it
    // Perform customizations to webpack config
    config.plugins.push(new webpack.IgnorePlugin(/\/__tests__\//))

    // Important: return the modified config
    return config
  },
}
```

## Useful Links

- [Custom webpack config Documentation](/docs/pages/api-reference/config/next-config-js/webpack)