Currently, the invalid USE dep report lists only the USE-dep string itself. This can really get confusing in a few corner cases: !!! All ebuilds that could satisfy "=pyopengl-3.0.2-r1::gentoo-cvs" have been masked. !!! One of the following masked packages is required to complete your request: - dev-python/pyopengl-3.0.2-r1::gentoo-cvs (masked by: invalid: DEPEND: Invalid atom (Invalid use dep: 'dev-python/python-exec[python_targets_python2_6?'), token 9) It took me a while to get that I've used the wrong variable and actually got: dev-python/setuptools[dev-python/python-exec[python... I think it would be helpful if portage printed the whole atom.