cc @aphearin - this should be good to go now, and maybe could be included in a quick bugfix release that fixes astropy 7.0 compatibility.

Thanks for this fix @bsipocz! I'm glad you were able to pinpoint this issue with setuptools, and separate this bug from the ongoing unresolved bug with Numpy 2.0 incompatibility, which may take longer to resolve. The source of the Numpy 2.0 incompatibility looks like the way the cython kernels are written, but I haven't gotten to the bottom of that yet. And so since your fix in this PR works in standalone fashion, maybe we should proceed with this merge and then turn attention to the cython/extension-helpers/etc - do you agree?

Yes, I agree that these should be handled separately. Saying that it's not yet numpy2.0 compatible is totally legitimate, but there is no reason for not to be astropy 7 compatible when it's all just silly API cleanups that shouldn't have happened without due notice of downstream.

Great, yes, that's what I thought too - thanks for confirming.