I'm very happy to accept that this is user error, either due to direct stupidity or indirectly by virtue of something I've done with macports (or using macports in the first place), but I can't figure out how to solve it. I've made a number of queries to the google oracle to no avail. I tried the stackoverflow suggestion of -m64 as well as -arch x86_64, but neither worked. Any suggestions? Thanks, Jeff Jeffs-MacBook-Pro:build-clang jhammond$ make make all-recursive Making all in /Users/jhammond/eclipse/MPICH2/mpich.git/build-clang/src/mpl make[2]: Nothing to be done for `all'. Making all in /Users/jhammond/eclipse/MPICH2/mpich.git/build-clang/src/openpa Making all in src make all-am Making all in test make[3]: Nothing to be done for `all'. make[3]: Nothing to be done for `all-am'. Making all in src/mpi/romio Making all in src/pm/hydra Making all in ../../mpl make[3]: Nothing to be done for `all'. Making all in tools/topo/hwloc/hwloc Making all in src make[4]: Nothing to be done for `all'. Making all in include make[4]: Nothing to be done for `all'. make[4]: Nothing to be done for `all-am'. Making all in . Making all in . CCLD src/env/mpichversion ld: warning: ld: warning: ignoring file /Users/jhammond/eclipse/MPICH2/mpich.git/build-clang/src/mpl/.libs/libmpl.a, file was built for archive which is not the architecture being linked (x86_64): /Users/jhammond/eclipse/MPICH2/mpich.git/build-clang/src/mpl/.libs/libmpl.aignoring file lib/.libs/libpmpich.a, file was built for archive which is not the architecture being linked (x86_64): lib/.libs/libpmpich.a ld: warning: ignoring file lib/.libs/libmpich.a, file was built for archive which is not the architecture being linked (x86_64): lib/.libs/libmpich.a ld: warning: ignoring file /Users/jhammond/eclipse/MPICH2/mpich.git/build-clang/lib/.libs/libmpich.a, file was built for archive which is not the architecture being linked (x86_64): /Users/jhammond/eclipse/MPICH2/mpich.git/build-clang/lib/.libs/libmpich.a Undefined symbols for architecture x86_64: "_MPIR_Version_CC", referenced from: _main in mpichversion.o "_MPIR_Version_CXX", referenced from: _main in mpichversion.o "_MPIR_Version_F77", referenced from: _main in mpichversion.o "_MPIR_Version_FC", referenced from: _main in mpichversion.o "_MPIR_Version_configure", referenced from: _main in mpichversion.o "_MPIR_Version_date", referenced from: _main in mpichversion.o "_MPIR_Version_device", referenced from: _main in mpichversion.o "_MPIR_Version_string", referenced from: _main in mpichversion.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) make[2]: *** [src/env/mpichversion] Error 1 make[1]: *** [all-recursive] Error 1 make: *** [all] Error 2 -- Jeff Hammond [email protected]