Unable to determine module type for application/source-map mime type

[tobad357]

What versions & operating system are you using?

Wrangler 4.22.0

Please provide a link to a minimal reproduction

No response

Describe the Bug

When trying to deploy to cloudflare with wrangler deploy we get the error

Unable to determine module type for application/source-map mime type

If we set --upload-source-maps=false then it goes away

Please provide any relevant error logs

--- 2025-07-02T07:46:56.554Z debug
Error: Unable to determine module type for application/source-map mime type
    at getModuleType (****node_modules/wrangler/wrangler-dist/cli.js:152060:13)
    at ****node_modules/wrangler/wrangler-dist/cli.js:152072:13
    at Array.map (<anonymous>)
    at convertWorkerBundleToModules (****node_modules/wrangler/wrangler-dist/cli.js:152071:33)
    at analyseBundle (****node_modules/wrangler/wrangler-dist/cli.js:152123:16)
    at handleStartupError (****node_modules/wrangler/wrangler-dist/cli.js:152244:28)
    at helpIfErrorIsSizeOrScriptStartup (****node_modules/wrangler/wrangler-dist/cli.js:152263:11)
    at deploy (****node_modules/wrangler/wrangler-dist/cli.js:152825:15)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async Object.handler (****node_modules/wrangler/wrangler-dist/cli.js:80948:66)

[petebacondarwin]

Would you be able to provide a simple Worker project that reproduces this issue?

[tobad357]

Sadly I can't, this is with a internal project and when I pick it apart it then works.
For reference it happened updating to latest zod version and we are having issues deploying due to long startup time if I remove minify.

I don't think those issues are related but worth mentioning

[petebacondarwin]

Ah! I just looked again at your stack trace.

I can see that you are trying to run wrangler deploy but it is getting an error back from Cloudflare saying that the script failed validation. This could be for a number of reasons but I suspect, given what you have said, it is because the startup time is too long.

As part of trying to aid diagnosis (helpIfErrorIsSizeOrScriptStartup()) we are then passing the Worker through an analysis phase (handleStartupError()) that tries to analyse the bundle contents (analyseBundle()).

It seems that this bit of code doesn't know how to handle the source-maps in the bundle output directory.

[petebacondarwin]

I think a reproduction could be to create a Worker with upload source maps turned on and then run wrangler check startup.