Hi everyone, Following a discussion today about C99 types in MPICH, we wanted to give a heads up. Since version 3.3, MPICH relies on many types which are technically optional in C99. For example uint64_t, uintptr_t, etc. In case it was not clear, platforms which do not provide these optional types are not supported by MPICH. The MPICH wiki page on C99 support has been updated to include this caveat: https://wiki.mpich.org/mpich/index.php/Shifting_toward_C99 Please let us know if you have any questions, comments, or concerns. Thanks, Ken