mg2d: do not pass NULL as a dummy MPI datatype

Use MPI_DATATYPE_NULL.

1 files changed, 1 insertions, 1 deletions

diff --git a/mg2d.c b/mg2d.c
index 9313ce3..1230dcf 100644
--- a/mg2d.c
+++ b/mg2d.c
@@ -1466,7 +1466,7 @@ MG2DContext *mg2d_solver_alloc_mpi(MPI_Comm comm, const size_t local_start[2],
     domainspec[4 * rank + 2] = local_size[0];
     domainspec[4 * rank + 3] = local_size[1];
 
-    MPI_Allgather(MPI_IN_PLACE, 0, NULL, domainspec, 4 * sizeof(*domainspec), MPI_BYTE, comm);
+    MPI_Allgather(MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, domainspec, 4 * sizeof(*domainspec), MPI_BYTE, comm);
     for (unsigned int proc = 0; proc < nb_processes; proc++) {
         size_t *proc_start = domainspec + 4 * proc;
         size_t *proc_size  = domainspec + 4 * proc + 2;