Yeah, it's definitely a hack. The argument for it, at best, is "practicality beats purity". The solution is two simple lines, but those lines need to be repeated in every project that depends on Tornado and cares about Windows, now or in the future. How many projects have to be affected to justify a hack like this? I'm not sure, but without this hack the add_reader methods, and by extension Tornado, will remain a compatibility trap.