Build fails on local module / monorepo-package as dependency

I’ve started a new project, a monorepo, which currently includes a design system as well as a website utilizing the modules of it. As the design system will only be used within the monorepo and won’t be made public I’d prefer not to publish it as a private npm module or similar.

Unfortunately this current situation leads to my builds failing on netlify while running just fine locally though. Does anyone have an idea how to get this working? Is there a way to tell netlify to install that module / monorepo-package from the git repo it got the website from?

Here the error from the build:

12:23:04 AM: npm ERR! code E404
12:23:04 AM: npm ERR! 404 Not Found - GET https://registry.npmjs.org/@project%2fdesign-system - Not found
12:23:04 AM: npm ERR! 404
12:23:04 AM: npm ERR! 404  '@project/design-system@1.0.0' is not in the npm registry.
12:23:04 AM: npm ERR! 404 You should bug the author to publish it (or use the name yourself!)

Untested, but, maybe you can keep the module’s files in the node_modules folder of your repo?