Thanks for the suggested patch and sorry that it has not been replied to earlier. As of Python 3.7, the libffi source for Unix-y platforms is no longer "vendored" in Python source releases; building ctypes now requires an external copy of libffi, either as supplied by the system, a third-party distribution, or by building yourself.  If changes to setup.py are still needed to build with a current external libffi, please feel free to reopen this issue with a pull request against the current master branch.