Unfortunately changing the tempfile call isn't an easy option for me. The situation in which I'm encountering the error is running tox on our project which is mounted in the /vagrant directory in the VM (this is standard for vagrant). Tox makes its own temp directory--presumably for test isolation--in the .tox directory in the project root. The actual call to tempfile.TemporaryFile() which is triggering the error is in a third party library that is called during a test run. 

I was able to work around the issue by changing the tox workdir setting to outside the mount. However, I'd like to mention that developing in vagrant in this fashion isn't uncommon and once 3.5 gains adoption I would guess this issue may affect a good number of people.

I'm happy to take a stab at writing a patch but looking at the code it's somewhat out of my comfort zone and I worry I'd make a hash of it.