vercel/next.js · error

Config options `skipProxyUrlNormalize` and `skipMiddlewareUr

Error message

Config options `skipProxyUrlNormalize` and `skipMiddlewareUrlNormalize` cannot be set at the same time. Please use `skipProxyUrlNormalize` instead.

What it means

Top-level `skipMiddlewareUrlNormalize` was renamed to `skipProxyUrlNormalize` (these are not under `experimental`). The check at config.ts:996-1003 forbids setting both, then aliases whichever single value is set into the other so the resolved config stays backward-compatible. Use the new `skipProxyUrlNormalize` key.

Source

Thrown at packages/next/src/server/config.ts:1000

    userConfig.experimental?.middlewarePrefetch !== undefined
  ) {
    throw new Error(
      'Config options `experimental.proxyPrefetch` and `experimental.middlewarePrefetch` cannot be set at the same time. Please use `experimental.proxyPrefetch` instead.'
    )
  }
  if (
    userConfig.experimental?.externalProxyRewritesResolve !== undefined &&
    userConfig.experimental?.externalMiddlewareRewritesResolve !== undefined
  ) {
    throw new Error(
      'Config options `experimental.externalProxyRewritesResolve` and `experimental.externalMiddlewareRewritesResolve` cannot be set at the same time. Please use `experimental.externalProxyRewritesResolve` instead.'
    )
  }
  if (
    userConfig.skipProxyUrlNormalize !== undefined &&
    userConfig.skipMiddlewareUrlNormalize !== undefined
  ) {
    throw new Error(
      'Config options `skipProxyUrlNormalize` and `skipMiddlewareUrlNormalize` cannot be set at the same time. Please use `skipProxyUrlNormalize` instead.'
    )
  }

  // Map Proxy config to Middleware config as it is currently an alias.
  if (
    userConfig.experimental?.proxyClientMaxBodySize === undefined &&
    userConfig.experimental?.middlewareClientMaxBodySize !== undefined
  ) {
    result.experimental.proxyClientMaxBodySize =
      userConfig.experimental.middlewareClientMaxBodySize
  }
  if (
    userConfig.experimental?.proxyPrefetch === undefined &&
    userConfig.experimental?.middlewarePrefetch !== undefined
  ) {
    result.experimental.proxyPrefetch =
      userConfig.experimental.middlewarePrefetch

View on GitHub (pinned to 0ae8c72462)

Solutions

1. Remove `skipMiddlewareUrlNormalize` and keep `skipProxyUrlNormalize`.
2. Re-run the build to confirm the URL-normalization skip is applied as intended.
3. Note this option lives at the top level, not inside `experimental`.

Example fix

// before
module.exports = { skipProxyUrlNormalize: true, skipMiddlewareUrlNormalize: true }
// after
module.exports = { skipProxyUrlNormalize: true }

if (config.skipProxyUrlNormalize !== undefined && config.skipMiddlewareUrlNormalize !== undefined) {
  throw new Error('set only skipProxyUrlNormalize (top-level, not experimental)');
}

When it happens

Trigger: Setting both `skipProxyUrlNormalize: true` and `skipMiddlewareUrlNormalize: true` at the top level of the config.

Common situations: Upgrading Next.js and adding the new key without deleting the old one. Sharing a config preset that still references the middleware name.

Related errors

• Config options `experimental.proxyClientMaxBodySize` and `ex
• Config options `experimental.proxyPrefetch` and `experimenta
• Config options `experimental.externalProxyRewritesResolve` a
• Client Max Body Size must be a valid number (bytes) or files
• Client Max Body Size must be larger than 0 bytes

AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/d8e0015c96148d5e. Report an issue: GitHub.