I maintain a Cython binding to some OCaml code (through their respective C interface). For past versions, I managed to cheat and distribute a wheel file for Windows through cross-compilation. Now, I finally managed a clean and native way to produce the library for Windows 64 bits. For the 32 bits cross-compiled version, I had a specific target in my setup.py with the proper commands to execute. Back on Windows, I would like to stick to a setuptoolsic way of doing, but the thing is I need to replace the regular linking command link.exe with a different tool (resp. flexlink.exe, shipped with OCaml on Windows) Don't panic: flexlink.exe just builds some assembler shit before compiling and linking with the regular link.exe. It is the proper way to link OCaml executables and shared libraries under Windows. For MacOS and Linux, the traditional Extension pattern works like a charm as follows (mlobject is produced by OCaml a bit earlier in the file after some timestamp checks, asmrunlib is the full path to the equivalent of python36.dll for OCaml) : extensions = [ Extension("foo", ["foo.pyx", "interface_c.c"], language="c", include_dirs=INCLUDE, extra_compile_args=compileargs, extra_link_args=[mlobject, asmrunlib, ] ) ] Let's say I limit myself to Python>=3.5, I guess (by comparison with too big projects like NumPy) I would need to start by extending distutils._msvccompiler.MSVCCompiler and replace the self.linker = _find_exe("link.exe", paths) with something based on flexlink.exe. The problem is that I have no idea how they manage the plumbing work that comes next (connecting this extended compiler and making it look like the regular msvc to the setup process). I suppose it is not thoroughly documented anywhere and that if they were able to do more than that in NumPy, I should be able to reach my goal somehow. My setup.py is still reasonably basic and a solution that keeps the whole building/packaging process in one single file would be great! Xavier (Question first asked here https://stackoverflow.com/q/42519377/1595335 before being advised this mailing-list)