Metadata 2.0 doesn't support versions that are a single number. This has recently been flagged as a pip issue (https://github.com/pypa/pip/pull/1445) because pip won't handle wheels with a single-component version. We can obviously accept the patch for pip as a backward-compatibility measure, but I'm not sure if that's a good idea. wheels, and much of the new pip functionality, is based around Metadata 2.0 and the new packaging PEPs, at least in principle, so I'd rather get a better view on why Metadata 2.0 doesn't accept these versions. Based on that, we can decide what to do in pip. As a data point, pywin32 uses a single-digit version and can't be built with the free MS compilers, so it would be an ideal candidate for distribution as a wheel. But I've seen nothing from the project indicating that they are even aware of wheels yet, and there may be good reasons why wheels won't work for them (registration of WIndows COM components, for example) So - should Metadata 2.0 allow single-number versions? Should we be advocating a version format change to projects like pywin32? If neither, what will be the impact (and do people have views on whether it's a serious enough issue to warrant pip special-casing this)? Thanks, Paul