Howdy! Sorry you're having trouble. To expedite your experience, provide some basics for me: Operating system: Python version: *Black* version: Does also happen on master: To answer the last question, follow these steps: * create a new virtualenv (make sure it's the same Python version); * clone this repository; * run `pip install -e .`; * make sure it's sane by running `python setup.py test`; and * run `black` like you did last time.