And another one:

..\Python\ceval.c(4271): warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data [C:\buildbot.python.org\3.x.kloth-win64\build\PCbuild\pythoncore.vcxproj]
..\Python\ceval.c(4459): warning C4244: '=' : conversion from 'Py_ssize_t' to 'int', possible loss of data [C:\buildbot.python.org\3.x.kloth-win64\build\PCbuild\pythoncore.vcxproj]

First in fast_function(), nd type is int:

    if (argdefs != NULL) {
        d = &PyTuple_GET_ITEM(argdefs, 0);
 ==>    nd = Py_SIZE(argdefs);  <=== HERE
    }
    return PyEval_EvalCodeEx((PyObject*)co, globals,
                             (PyObject *)NULL, (*pp_stack)-n, na,
                             (*pp_stack)-2*nk, nk, d, nd, kwdefs,
                             PyFunction_GET_CLOSURE(func));

Second in ext_do_call(), nstar type is int:

        nstar = PyTuple_GET_SIZE(stararg);

Must check: Py_SIZE(argdefs) <= INT_MAX and PyTuple_GET_SIZE(stararg) <= INT_MAX.