nextjs - 💡(How to fix) Fix [Turbopack] "TypeError: fetch failed" with cause "not implemented... yet..." during SSG build on Vercel [1 comments, 2 participants]

Link to the code that reproduces this issue

https://github.com/laststance/laststance.io

Vercel Deployment with error: https://laststance-q3fkodkgx-ryota-murakamis-projects.vercel.app

Commit with Turbopack build: 3c53a0b17f48be3724e43a43b066a43e4e536e6c

To Reproduce

This issue only occurs in Vercel's build environment, not locally.

1. Fork or clone the repository: git clone https://github.com/laststance/laststance.io
2. Checkout the commit with Turbopack: git checkout 3c53a0b
3. Deploy to Vercel (the error occurs during build)
4. Check Vercel build logs for the error during "Collecting page data" and "Generating static pages" phases

Note: Running next build locally does NOT reproduce this error. The error only manifests in Vercel's Ubuntu Linux build environment.

Current vs. Expected behavior

Current behavior: During next build with Turbopack on Vercel, the following error is logged:

TypeError: fetch failed
at ignore-listed frames {
[cause]: Error: not implemented... yet...
at module evaluation (.next/server/chunks/_c764c392._.js:2:1127)
at instantiateModule (.next/server/chunks/[turbopack]_runtime.js:715:9)
}

This error occurs during:

1. "Collecting page data" phase
2. "Generating static pages" phase

The build completes successfully (all pages generated), but the error is thrown as an unhandled promise rejection. This causes error monitoring tools (like Sentry) to capture it as an issue.

Expected behavior: No unhandled "not implemented... yet..." errors should be thrown during a successful build.

Provide environment information

Vercel Build Environment (where error occurs):

Platform: Ubuntu Linux 24.04
Node: v20.19.6
Next.js: 16.0.7 (Turbopack)
Build Machine: 2 cores, 8 GB (iad1 region)

Local Environment (error does NOT occur):

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.1.0
Binaries:
  Node: 22.18.0
  pnpm: 10.24.0
Relevant Packages:
  next: 16.0.7
  react: 19.2.1
  react-dom: 19.2.1
  typescript: 5.9.3

Which area(s) are affected? (Select all that apply)

Turbopack

Which stage(s) are affected? (Select all that apply)

next build (build)

Additional context

Vercel Build Log excerpt:

2025-12-05T11:16:52.623Z  Running build in Washington, D.C., USA (East) – iad1
2025-12-05T11:16:52.624Z  Build machine configuration: 2 cores, 8 GB
2025-12-05T11:17:05.063Z  ▲ Next.js 16.0.7 (Turbopack)
2025-12-05T11:17:39.936Z  ✓ Compiled successfully in 33.5s
2025-12-05T11:17:53.788Z  Collecting page data using 1 worker ...
2025-12-05T11:17:54.118Z  TypeError: fetch failed
2025-12-05T11:17:54.118Z  at ignore-listed frames {
2025-12-05T11:17:54.118Z  [cause]: Error: not implemented... yet...
2025-12-05T11:17:54.118Z  at module evaluation (.next/server/chunks/_c764c392._.js:2:1127)
2025-12-05T11:17:54.119Z  at instantiateModule (.next/server/chunks/[turbopack]_runtime.js:715:9)
2025-12-05T11:17:54.119Z  }
2025-12-05T11:17:54.496Z  Generating static pages using 1 worker (0/37) ...
2025-12-05T11:17:54.835Z  TypeError: fetch failed
2025-12-05T11:17:54.835Z  at ignore-listed frames {
2025-12-05T11:17:54.836Z  [cause]: Error: not implemented... yet...
2025-12-05T11:17:54.836Z  at d (.next/server/chunks/ssr/027a9_next_dist_1bdaf56b._.js:5:27460)
2025-12-05T11:17:54.837Z  }
2025-12-05T11:18:04.651Z  ✓ Generating static pages using 1 worker (37/37) in 10.2s

Project dependencies that may be relevant:

• code-inspector-plugin with Turbopack configuration
• @sentry/nextjs for error monitoring
• @next/mdx for MDX blog posts
• GitHub API calls during SSG via octokit

Workaround: Using next build --webpack instead of Turbopack avoids the error:

{
  "scripts": {
    "build": "next build --webpack"
  }
}

The error appears to be internal to Turbopack's module loading mechanism, specific to Vercel's Linux build environment.