vercel/next.js · error

The "${key}" option has been modified. ${customMessage ? cus

Error message

The "${key}" option has been modified. ${customMessage ? customMessage + '. ' : ''}It should be removed from your ${configFileName}.

What it means

Warning from warnCustomizedOption during config load: it walks the dotted key path through the user's config and compares the found value against the known default. A value that differs from the default means the user customized an option Next.js no longer reads (its behavior is fixed now), so the warning — with an optional custom explanation — asks for its removal from the config file.

Source

Thrown at packages/next/src/server/config.ts:335

  key: string,
  defaultValue: any,
  customMessage: string,
  configFileName: string,
  silent: boolean
) {
  const segs = key.split('.')
  let current = config

  while (segs.length >= 1) {
    const seg = segs.shift()!
    if (!(seg in current)) {
      return
    }
    current = (current as any)[seg]
  }

  if (!silent && current !== defaultValue) {
    Log.warn(
      `The "${key}" option has been modified. ${customMessage ? customMessage + '. ' : ''}It should be removed from your ${configFileName}.`
    )
  }
}

/**
 * Assigns defaults to the user config and validates the config.
 *
 * @param dir - The directory of the project.
 * @param userConfig - The user config.
 * @param silent - Whether to suppress warnings.
 * @returns The complete config.
 */
function assignDefaultsAndValidate(
  dir: string,
  userConfig: NextConfig & { configFileName: string },
  silent: boolean,
  phase: PHASE_TYPE

View on GitHub (pinned to 258b1c1bc0)

Solutions

1. Remove the modified/deprecated option from your next.config file.

When it happens

Trigger: Thrown at packages/next/src/server/config.ts:302 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of vercel/next.js@258b1c1bc0 (2026-08-19). Data as JSON: /api/errors/e1dbe5931e0c372d. Report an issue: GitHub.