Hello Howard, I have encountered the same problem with mpich-3.0.1 today. (And that's why I found this thread :P) After raising the optimization level, it didn't complain about that undeclared problem anymore, and the installation goes well. This is my configure option: ./configure --prefix /opt/app/MPICH --enable-fast=all,O3 BTW, the problem still exist for "indexed-misc.c" under the test directory Regards