Specified i18n.domains must be an array of domain objects e.

Error message

Specified i18n.domains must be an array of domain objects e.g. [ { domain: 'example.fr', defaultLocale: 'fr', locales: ['fr'] } ] received ${typeof i18n.domains}.
See more info here: https://nextjs.org/docs/messages/invalid-i18n-config

What it means

Thrown when `i18n.domains` is defined but is not an array. Domains are an optional feature for serving different locales from different hostnames; the validator at config.ts:1227 only checks `typeof i18n.domains !== 'undefined' && !Array.isArray(i18n.domains)`, so `undefined` is allowed but any other non-array type fails.

Source

Thrown at packages/next/src/server/config.ts:1228

      )
    }

    if (i18n.locales.length > 100 && !silent) {
      Log.warn(
        `Received ${i18n.locales.length} i18n.locales items which exceeds the recommended max of 100.\nSee more info here: https://nextjs.org/docs/advanced-features/i18n-routing#how-does-this-work-with-static-generation`
      )
    }

    const defaultLocaleType = typeof i18n.defaultLocale

    if (!i18n.defaultLocale || defaultLocaleType !== 'string') {
      throw new Error(
        `Specified i18n.defaultLocale should be a string.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    if (typeof i18n.domains !== 'undefined' && !Array.isArray(i18n.domains)) {
      throw new Error(
        `Specified i18n.domains must be an array of domain objects e.g. [ { domain: 'example.fr', defaultLocale: 'fr', locales: ['fr'] } ] received ${typeof i18n.domains}.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    if (i18n.domains) {
      const invalidDomainItems = i18n.domains.filter((item) => {
        if (!item || typeof item !== 'object') return true
        if (!item.defaultLocale) return true
        if (!item.domain || typeof item.domain !== 'string') return true

        if (item.domain.includes(':')) {
          console.warn(
            `i18n domain: "${item.domain}" is invalid it should be a valid domain without protocol (https://) or port (:3000) e.g. example.vercel.sh`
          )
          return true
        }

        const defaultLocaleDuplicate = i18n.domains?.find(

View on GitHub (pinned to 0ae8c72462)

Solutions

Wrap domain definitions in an array: `domains: [{ domain: 'example.fr', defaultLocale: 'fr', locales: ['fr'] }]`.
Remove the `domains` key entirely if you are not using per-domain locale routing.

Example fix

// before
module.exports = { i18n: { locales: ['fr','en'], defaultLocale: 'en', domains: { domain: 'example.fr', defaultLocale: 'fr' } } }
// after
module.exports = { i18n: { locales: ['fr','en'], defaultLocale: 'en', domains: [{ domain: 'example.fr', defaultLocale: 'fr', locales: ['fr'] }] } }

Defensive patterns

Strategy: validation

Validate before calling

if (i18n.domains !== undefined && !Array.isArray(i18n.domains)) {
  throw new Error('i18n.domains must be an array or undefined');
}

Type guard

function hasValidDomains(i18n: any): boolean {
  return i18n.domains === undefined || Array.isArray(i18n.domains);
}

Prevention

Only add `domains` when using per-hostname locale routing; otherwise omit it.
Always wrap domain entries in an array literal.

When it happens

Trigger: Setting `i18n: { domains: { domain: 'example.fr', defaultLocale: 'fr' } }` (a single object instead of an array); `domains: 'example.fr'`; `domains: false`.

Common situations: Misreading the docs and providing a single domain object instead of a list; merging configs that overwrite the array with a scalar; converting from a YAML/JSON config that serializes a single item as an object.

Related errors

AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/e1da86306f275de8. Report an issue: GitHub.