I was hoping someone with more perl wisdom would know where to look and what to look for. Thank you haukex! ExtUtils::Installed->modules() outputs module names (and apparently the occasional dist, oops) and Module::Metadata reads module names or files (but not dists). These core modules are very reliable and designed to work together. Anyway when ExtUtils::Installed->modules() sends a dist name to Module::Metadata->new_from_module() and the lookup fails, the solution is to send that dist name back to ExtUtils::Installed->files() to get a list of the module files, which Module::Metadata->new_from_file() understands. Thank you for helping me realize what's happening and fix a very old and annoying bug (in my code).