I assume this was supposed to be Py_ssize_t since there are no uses of plain ssize_t.

Include/longobject.h

@@ -21,7 +21,7 @@ PyAPI_FUNC(PyObject *) PyLong_FromSize_t(size_t);
 PyAPI_FUNC(PyObject *) PyLong_FromSsize_t(Py_ssize_t);
 PyAPI_FUNC(PyObject *) PyLong_FromDouble(double);
 PyAPI_FUNC(long) PyLong_AsLong(PyObject *);
-PyAPI_FUNC(ssize_t) PyLong_AsSsize_t(PyObject *);
+PyAPI_FUNC(Py_ssize_t) PyLong_AsSsize_t(PyObject *);
 PyAPI_FUNC(size_t) PyLong_AsSize_t(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLong(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLongMask(PyObject *);