PIO fails to build with "size_t and long long must be the same size!"

On macports toolchain gFortran/openmpi PIO fails to build:

CMake Error at src/clib/CMakeLists.txt:180 (message):
  size_t and long long must be the same size!


-- Configuring incomplete, errors occurred!
See also "/Users/Lemmen/devel/esmf/esmf-code/src/Infrastructure/IO/PIO/Build/CMakeFiles/CMakeOutput.log".