Next.js · sdk · fg-0297

Build fails on Next.js 16 because a parallel route slot has no default.js

Missing required default.js file for parallel route at app/@modal

Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100

Cause

Next.js 16 requires an explicit default.js in every parallel route slot. Earlier versions fell back quietly when a slot had no match on hard navigation.

Fix

Add default.tsx to each slot that returns null, or calls notFound() if that is the intended behavior.

Apply

// app/@modal/default.tsx
export default function Default() {
  return null
}

Affects: Next.js 16.0 and later, App Router parallel routes

Sources

• https://nextjs.org/docs/app/guides/upgrading/version-16
• https://nextjs.org/docs/app/api-reference/file-conventions/parallel-routes

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