[BUG] Failed to set to read-only cache for SSG site

[Dramelac]

Describe the bug

I have an SSG Next.js site hosted on Cloudflare worker. The site works fine but it is not using cache.

I tried to use the static cache as explained here: https://opennext.js.org/cloudflare/caching#ssg-site but on each invocation I have an error log with message:"Failed to set to read-only cache".

Did I miss something ?

Steps to reproduce

On open-next.config.ts I have:

import { defineCloudflareConfig } from "@opennextjs/cloudflare";
import staticAssetsIncrementalCache from "@opennextjs/cloudflare/overrides/incremental-cache/static-assets-incremental-cache";

export default defineCloudflareConfig({
  incrementalCache: staticAssetsIncrementalCache,
  enableCacheInterception: true,
});

On my wrangler config I have:

• A worker self reference:

"services": [
  {
    "binding": "WORKER_SELF_REFERENCE",
    "service": "site-dev"
  }
]

• I have a reference to assets

"assets": {
    "directory": ".open-next/assets",
    "binding": "ASSETS"
  }

• I'm not sure if this is needed for SSG cache (doc is not very precise about SSG caching) but I tried to create and bind an R2 cache bucket but it didn't change anything:

"r2_buckets": [
  {
    "binding": "NEXT_INC_CACHE_R2_BUCKET",
    "bucket_name": "dev-cache-web-dashboard"
  }
]

I also have enabled logs to see the error message but there isn't any details on why the cache failed.

Expected behavior

The site works as intended using cache without error log.

@opennextjs/cloudflare version

1.6.2

Wrangler version

4.26.0

next info output

My application is deployed with cloudflare build.

Relevant Packages:
  next: 15.3.5 // There is a newer version (15.4.5) available, upgrade recommended!
  eslint-config-next: 15.2.4
  react: 19.1.1
  react-dom: 19.1.1
  typescript: 5.8.3
Next.js Config:
  output: N/A

Additional context

Thank you for the help!

[vicb]

The error means that something is writing to your cache

[Dramelac]

What would write to the cache ?
I only have static pages..

After build, only static pages:

[vicb]

Try to add NEXT_PRIVATE_DEBUG_CACHE=1 in your .env and you should see

[Dramelac]

Nothing much to see ...

[Dramelac]

Any idea why @vicb ?

[conico974]

What would write to the cache ? I only have static pages..

After build, only static pages:

This doesn't mean that your page is SSG, you get the same thing for ISR route, which are not static.
The incremental cache is also used for the data cache ("use cache", unstacle_cache or the fetch cache)

If none of those apply to you, and that your route are indeed SSG, then you'll need to provide a reproduction