[BUG] Can't get the official Nextjs sample MDX approach to work with workers

[mohsentaleb]

I’m trying to get the official Next.js sample for rendering a basic MDX file to work in a workerd environment, but I keep running into the following error:

[wrangler:info] Ready on http://localhost:8787
✘ [ERROR] Uncaught Error: Internal: NoFallbackError Error

I’ve created a minimal reproduction repo here for the team to review:
👉 https://github.com/mohsentaleb/mdx-open-next/tree/next/mdx

Would appreciate any guidance or fixes here 🙏

Steps to reproduce

1. Clone the repo above.
2. Install dependencies.
3. Run the project in workerd using Wrangler (npx wrangler dev) or run npm run preview.
4. Visit the /articles/welcome page.

Expected behavior

The articles/welcome page should render an MDX file correctly, just like it does when using the standard Next.js build workflow.

@opennextjs/cloudflare version

1.9.0

Wrangler version

4.40.2

next info output

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP PREEMPT_DYNAMIC Thu Jun  5 18:30:46 UTC 2025
  Available memory (MB): 32008
  Available CPU cores: 20
Binaries:
  Node: 20.19.0
  npm: 10.8.2
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  next: 15.5.4 // Latest available version is detected (15.5.4).
  eslint-config-next: 15.5.4
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.9.2
Next.js Config:
  output: N/A

Additional context

• The articles page imports an MDX file using the passed slug.
• generateStaticParams is correctly set up so the page can be generated at build time.
• The same setup works flawlessly with the standard Next.js build, but not in workerd env.

[sommeeeer]

You probably need to configure caching. For a SSG site you can use: https://opennext.js.org/cloudflare/caching#ssg-site

I recommend reading that entire page on caching.

[vicb]

There are 2 reasons why this might not work at runtime:

• while workerd (Cloudflare runtime) recently added a node:fs implementation, you would need to add the mdx as external modules which requires some configuration
• I think MDXRemote is based on eval which is not supported by workerd at the moment.

If you generate the cache at build time (next dev) you should be able to serve the cache content but you will not be able to revalidate it.

@dario-piotrowicz has a setup that works with 3rd libs (not using eval), He'll add something to the docs when he can find some time.

Hope this helps

[cording12]

It's not what you have asked, but I've had success using Fumadocs in a Worker - no issues at all. Could be an alternative if you can't get this to work.

Edit: I've just open sourced my project - you can see the docs site in next-cloudflare-turbo