The odd thing is that it's working fine for a more complex component in the same subsystem. Perhaps just a particular dependency causing classpath conflicts?

Adding [fipp "0.6.24"] as a dev dependency helped but I'm not sure what's going on.

@U06BE1L6T you typically have the dependency listed somewhere in your lein :dependencies - such as the dev profile as you said. Then you also add the checkouts.

I don’t think you can just use checkouts with no actual :dependencies declaration anywhere

The think is that the module I depend on (call it A) via checkouts ( and of course it’s also listed as a regular dependency in project.clj) depends on fipp but only as “dev” dependency (such as when running lein repl ) so it’s states in :dependencies of the dev profile in that module’s project.clj And while this works fine when not using checkouts, with them it forces me to also list fipp in the dev prodile in the main module (call it B). So I know need to repeat all the dev dependencies of module A in module B