diff --git a/patches/amber14.diff/AmberTools/src/sander/runmd.F90 b/patches/amber14.diff/AmberTools/src/sander/runmd.F90
index af3bc6f6f8c57c788754fafe769faa48d8ed1d73..42ed0e4c60a5f080aee82c457af6029f627b94cd 100644
--- a/patches/amber14.diff/AmberTools/src/sander/runmd.F90
+++ b/patches/amber14.diff/AmberTools/src/sander/runmd.F90
@@ -327,7 +327,7 @@ subroutine runmd(xx,ix,ih,ipairs,x,winv,amass,f, &
 
 ! variables for plumed
    _REAL_ :: plumed_box(3,3),plumed_virial(3,3), plumed_kbt
-   integer :: plumed_version,plumed_stopflag,plumed_ms
+   integer :: plumed_version,plumed_stopflag,plumed_ms,plumed_ss,plumed_ws
    _REAL_ :: plumed_energyUnits,plumed_timeUnits,plumed_lengthUnits
 
    !==========================================================================
@@ -767,9 +767,21 @@ subroutine runmd(xx,ix,ih,ipairs,x,winv,amass,f, &
      call plumed_f_gcmd("setMPIFComm"//char(0),commsander)
      if(master)then
        call mpi_comm_size(commmaster,plumed_ms,ierr)
+     else
+       plumed_ms=1
      endif
      call mpi_bcast(plumed_ms,1,MPI_INTEGER,0,commsander,ierr)
-     if(plumed_ms>1)then
+     call mpi_comm_size(commsander,plumed_ss,ierr)
+     call mpi_comm_size(commworld,plumed_ws,ierr)
+! this is a hack that is necessary to detect multiple replicas
+! commworld: all processors
+! commsander: group related to a single replica
+! commmaster: with replicas, group with the master of each replica
+!             without replicas, group with all processors
+! thus, to detect multiple replicas, I check that
+! size(commworld)==size(commmaster)*size(commsander)
+! and at the same time size(commaster)>1
+     if(plumed_ms>1 .and. plumed_ws==plumed_ms*plumed_ss)then
        call plumed_f_gcmd("GREX setMPIFIntracomm"//char(0),commsander)
        if(master) then
          call plumed_f_gcmd("GREX setMPIFIntercomm"//char(0),commmaster)