"Cythonize" not working on OSX?

Hi all, As others have noted (see e.g. here<https://github.com/scikit-image/scikit-image/pull/873#issuecomment-33875298>), the change from using a cython command to the "cythonize" function call within skimage/_build.py has broken the build process on some machines. Cython files don't get compiled to .c files automatically and the build fails with errors such as: clang: error: no such file or directory: 'orb_cy.c' clang: error: no input files clang: error: no such file or directory: 'orb_cy.c' clang: error: no input files Calling Cython manually for all the files works, but obviously this is not a solution. Does anyone know what's going on here? Juan.