Hi, I have a problem using mpi_type_create_f90_real: I can compile the attached code but when I run it I get $ mpiexec -n 1 ./mpitest Fatal error in MPI_Allreduce: Invalid MPI_Op, error stack: MPI_Allreduce(861)......: MPI_Allreduce(sbuf=0x7fff02a4eec0, rbuf=0x7fff02a4eed0, count=1, dtype=USER<f90_real>, MPI_SUM, MPI_COMM_WORLD) failed MPIR_SUM_check_dtype(97): MPI_Op MPI_SUM operation not defined for this datatype I am using: $ mpif90 -v mpif90 for MPICH2 version 1.5 Is this a problem in my use of mpi_type_create_f90_real or in mpich? Thanks, Marco program mpitest use mpi implicit none integer, parameter :: wp = selected_real_kind(12,307) integer, parameter :: & wp_p = precision(1.0_wp), & wp_r = range(1.0_wp) integer :: wp_mpi, mpi_id, ierr real(wp) :: res ! MPI setup call mpi_init(ierr) call mpi_comm_rank(mpi_comm_world,mpi_id,ierr) !wp_mpi = mpi_double_precision ! works fine call mpi_type_create_f90_real(wp_p,wp_r,wp_mpi,ierr) call mpi_allreduce( real(mpi_id,wp) , res , 1 , & wp_mpi,mpi_sum,mpi_comm_world, ierr) write(*,*) "res = ",res call mpi_finalize(ierr) end program mpitest