The patch is missing the "errors" parameter of PyUnicode_DecodeLocale. But it should call PyUnicode_DecodeMBCS instead. In the "C" locale, PyUnicode_DecodeLocale is Latin-1 because the CRT mbstowcs just casts the values to wchar_t. socket_getnameinfo also decodes as UTF-8: >>> socket.getnameinfo(('127.0.0.1', 20), 0) Traceback (most recent call last): File "<stdin>", line 1, in <module> UnicodeDecodeError: 'utf-8' codec can't decode byte 0x82 in position 0: invalid start byte Steve, does your suggestion include reimplementing socket.gethostbyaddr and socket.gethostbyname_ex using GetNameInfoW and GetAddrInfoW? gethostbyaddr and gethostbyname are deprecated and lack a Unicode implementation.