diff --git a/Grid/communicator/SharedMemoryMPI.cc b/Grid/communicator/SharedMemoryMPI.cc
index 4b440fc0..6089093b 100644
--- a/Grid/communicator/SharedMemoryMPI.cc
+++ b/Grid/communicator/SharedMemoryMPI.cc
@@ -666,7 +666,6 @@ void GlobalSharedMemory::SharedMemoryAllocate(uint64_t bytes, int flags)
 #endif
       void * ptr =  mmap(NULL,size, PROT_READ | PROT_WRITE, mmap_flag, fd, 0);
       
-      //      std::cout << "Set WorldShmCommBufs["<<r<<"]="<<ptr<< "("<< size<< "bytes)"<<std::endl;
       if ( ptr == (void * )MAP_FAILED ) {       
 	perror("failed mmap");     
 	assert(0);    
@@ -772,11 +771,13 @@ void SharedMemory::SetCommunicator(Grid_MPI_Comm comm)
   std::vector<int> ranks(size);   for(int r=0;r<size;r++) ranks[r]=r;
   MPI_Group_translate_ranks (FullGroup,size,&ranks[0],ShmGroup, &ShmRanks[0]); 
 
-#if 0
+#ifdef GRID_SHM_FORCE_MPI
   // Hide the shared memory path between ranks
   {
     for(int r=0;r<size;r++){
-      ShmRanks[r] = MPI_UNDEFINED;
+      if ( r!=rank ) {
+	ShmRanks[r] = MPI_UNDEFINED;
+      }
     }
   }
 #endif
diff --git a/configure.ac b/configure.ac
index ad3692ee..a387be8a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -550,6 +550,15 @@ AC_ARG_ENABLE([shmpath],[AC_HELP_STRING([--enable-shmpath=path],
 	      [ac_SHMPATH=/var/lib/hugetlbfs/global/pagesize-2MB/])
 AC_DEFINE_UNQUOTED([GRID_SHM_PATH],["$ac_SHMPATH"],[Path to a hugetlbfs filesystem for MMAPing])
 
+############### force MPI in SMP
+AC_ARG_ENABLE([shm-force-mpi],[AC_HELP_STRING([--enable-shm-force-mpi],
+              [Force MPI within shared memory])],[ac_SHM_FORCE_MPI=${enable_shm_force_mpi}],[ac_SHM_FORCE_MPI=no])
+case ${ac_SHM_FORCE_MPI} in
+     yes)
+        AC_DEFINE([GRID_SHM_FORCE_MPI],[1],[GRID_SHM_FORCE_MPI] )
+      ;;
+     *) ;;
+esac
 
 ############### communication type selection
 AC_ARG_ENABLE([comms-threads],[AC_HELP_STRING([--enable-comms-threads | --disable-comms-threads],