diff --git a/src/fix_heat.cpp b/src/fix_heat.cpp
index 97e0ed6a7..846531dbb 100644
--- a/src/fix_heat.cpp
+++ b/src/fix_heat.cpp
@@ -1,344 +1,344 @@
 /* ----------------------------------------------------------------------
    LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
    http://lammps.sandia.gov, Sandia National Laboratories
    Steve Plimpton, sjplimp@sandia.gov
 
    Copyright (2003) Sandia Corporation.  Under the terms of Contract
    DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
    certain rights in this software.  This software is distributed under
    the GNU General Public License.
 
    See the README file in the top-level LAMMPS directory.
 ------------------------------------------------------------------------- */
 
 /* ----------------------------------------------------------------------
    Contributing author: Paul Crozier (SNL)
 ------------------------------------------------------------------------- */
 
 #include <math.h>
 #include <stdlib.h>
 #include <string.h>
 #include "fix_heat.h"
 #include "atom.h"
 #include "domain.h"
 #include "region.h"
 #include "group.h"
 #include "force.h"
 #include "update.h"
 #include "modify.h"
 #include "input.h"
 #include "variable.h"
 #include "memory.h"
 #include "error.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
 
 enum{CONSTANT,EQUAL,ATOM};
 
 /* ---------------------------------------------------------------------- */
 
 FixHeat::FixHeat(LAMMPS *lmp, int narg, char **arg) : Fix(lmp, narg, arg),
 idregion(NULL), hstr(NULL), vheat(NULL), vscale(NULL)
 {
   if (narg < 4) error->all(FLERR,"Illegal fix heat command");
 
   scalar_flag = 1;
   global_freq = 1;
   extscalar = 0;
 
   nevery = force->inumeric(FLERR,arg[3]);
   if (nevery <= 0) error->all(FLERR,"Illegal fix heat command");
 
   hstr = NULL;
 
   if (strstr(arg[4],"v_") == arg[4]) {
     int n = strlen(&arg[4][2]) + 1;
     hstr = new char[n];
     strcpy(hstr,&arg[4][2]);
   } else {
     heat_input = force->numeric(FLERR,arg[4]);
     hstyle = CONSTANT;
   }
 
   // optional args
 
   iregion = -1;
 
   int iarg = 5;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"region") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix heat command");
       iregion = domain->find_region(arg[iarg+1]);
       if (iregion == -1)
         error->all(FLERR,"Region ID for fix heat does not exist");
       int n = strlen(arg[iarg+1]) + 1;
       idregion = new char[n];
       strcpy(idregion,arg[iarg+1]);
       iarg += 2;
     } else error->all(FLERR,"Illegal fix heat command");
   }
 
   scale = 1.0;
 
   maxatom = 0;
 }
 
 /* ---------------------------------------------------------------------- */
 
 FixHeat::~FixHeat()
 {
   delete [] hstr;
   delete [] idregion;
   memory->destroy(vheat);
   memory->destroy(vscale);
 }
 
 /* ---------------------------------------------------------------------- */
 
 int FixHeat::setmask()
 {
   int mask = 0;
   mask |= END_OF_STEP;
   return mask;
 }
 
 /* ---------------------------------------------------------------------- */
 
 void FixHeat::init()
 {
   // set index and check validity of region
 
   if (iregion >= 0) {
     iregion = domain->find_region(idregion);
     if (iregion == -1)
       error->all(FLERR,"Region ID for fix heat does not exist");
   }
 
   // check variable
 
   if (hstr) {
     hvar = input->variable->find(hstr);
     if (hvar < 0)
       error->all(FLERR,"Variable name for fix heat does not exist");
     if (input->variable->equalstyle(hvar)) hstyle = EQUAL;
     else if (input->variable->atomstyle(hvar)) hstyle = ATOM;
     else error->all(FLERR,"Variable for fix heat is invalid style");
   }
 
   // check for rigid bodies in region (done here for performance reasons)
-  if (modify->check_rigid_region_overlap(groupbit,domain->regions[iregion]))
+  if (iregion >= 0 && modify->check_rigid_region_overlap(groupbit,domain->regions[iregion]))
     error->warning(FLERR,"Cannot apply fix heat to atoms in rigid bodies");
 
   // cannot have 0 atoms in group
 
   if (group->count(igroup) == 0)
     error->all(FLERR,"Fix heat group has no atoms");
   masstotal = group->mass(igroup);
   if (masstotal <= 0.0)
     error->all(FLERR,"Fix heat group has invalid mass");
 }
 
 /* ---------------------------------------------------------------------- */
 
 void FixHeat::end_of_step()
 {
   int i;
   double heat,ke,massone;
   double vsub[3],vcm[3];
 
   double **x = atom->x;
   double **v = atom->v;
   int *mask = atom->mask;
   int nlocal = atom->nlocal;
   int *type = atom->type;
   double *mass = atom->mass;
   double *rmass = atom->rmass;
 
   // reallocate per-atom arrays if necessary
 
   if (hstyle == ATOM && atom->nmax > maxatom) {
     maxatom = atom->nmax;
     memory->destroy(vheat);
     memory->destroy(vscale);
     memory->create(vheat,maxatom,"heat:vheat");
     memory->create(vscale,maxatom,"heat:vscale");
   }
 
   // evaluate variable
 
   if (hstyle != CONSTANT) {
     modify->clearstep_compute();
     if (hstyle == EQUAL) heat_input = input->variable->compute_equal(hvar);
     else input->variable->compute_atom(hvar,igroup,vheat,1,0);
     modify->addstep_compute(update->ntimestep + nevery);
   }
 
   // vcm = center-of-mass velocity of scaled atoms
 
   if (iregion < 0) {
     ke = group->ke(igroup)*force->ftm2v;
     group->vcm(igroup,masstotal,vcm);
   } else {
     masstotal = group->mass(igroup,iregion);
     if (masstotal == 0.0) error->all(FLERR,"Fix heat group has no atoms");
     ke = group->ke(igroup,iregion)*force->ftm2v;
     group->vcm(igroup,masstotal,vcm,iregion);
   }
   double vcmsq = vcm[0]*vcm[0] + vcm[1]*vcm[1] + vcm[2]*vcm[2];
 
   // add heat via scale factor on velocities for CONSTANT and EQUAL cases
   // scale = velocity scale factor to accomplish eflux change in energy
   // vsub = velocity subtracted from each atom to preserve momentum
   // overall KE cannot go negative
 
   Region *region = NULL;
   if (iregion >= 0) {
     region = domain->regions[iregion];
     region->prematch();
   }
 
   if (hstyle != ATOM) {
     heat = heat_input*nevery*update->dt*force->ftm2v;
     double escale =
       (ke + heat - 0.5*vcmsq*masstotal)/(ke - 0.5*vcmsq*masstotal);
     if (escale < 0.0) error->all(FLERR,"Fix heat kinetic energy went negative");
     scale = sqrt(escale);
     vsub[0] = (scale-1.0) * vcm[0];
     vsub[1] = (scale-1.0) * vcm[1];
     vsub[2] = (scale-1.0) * vcm[2];
 
     if (iregion < 0) {
       for (i = 0; i < nlocal; i++)
         if (mask[i] & groupbit) {
           v[i][0] = scale*v[i][0] - vsub[0];
           v[i][1] = scale*v[i][1] - vsub[1];
           v[i][2] = scale*v[i][2] - vsub[2];
         }
     } else {
       for (int i = 0; i < nlocal; i++)
         if (mask[i] & groupbit && region->match(x[i][0],x[i][1],x[i][2])) {
           v[i][0] = scale*v[i][0] - vsub[0];
           v[i][1] = scale*v[i][1] - vsub[1];
           v[i][2] = scale*v[i][2] - vsub[2];
         }
     }
 
   // add heat via per-atom scale factor on velocities for ATOM case
   // vscale = velocity scale factor to accomplish eflux change in energy
   // vsub = velocity subtracted from each atom to preserve momentum
   // KE of an atom cannot go negative
 
   } else {
     vsub[0] = vsub[1] = vsub[2] = 0.0;
     if (iregion < 0) {
       for (i = 0; i < nlocal; i++) {
         if (mask[i] & groupbit) {
           heat = vheat[i]*nevery*update->dt*force->ftm2v;
           vscale[i] =
             (ke + heat - 0.5*vcmsq*masstotal)/(ke - 0.5*vcmsq*masstotal);
           if (vscale[i] < 0.0)
             error->all(FLERR,
                        "Fix heat kinetic energy of an atom went negative");
           scale = sqrt(vscale[i]);
           if (rmass) massone = rmass[i];
           else massone = mass[type[i]];
           vsub[0] += (scale-1.0) * v[i][0]*massone;
           vsub[1] += (scale-1.0) * v[i][1]*massone;
           vsub[2] += (scale-1.0) * v[i][2]*massone;
         }
       }
 
       vsub[0] /= masstotal;
       vsub[1] /= masstotal;
       vsub[2] /= masstotal;
 
       for (i = 0; i < nlocal; i++)
         if (mask[i] & groupbit) {
           scale = sqrt(vscale[i]);
           v[i][0] = scale*v[i][0] - vsub[0];
           v[i][1] = scale*v[i][1] - vsub[1];
           v[i][2] = scale*v[i][2] - vsub[2];
         }
 
     } else {
       for (i = 0; i < nlocal; i++) {
         if (mask[i] & groupbit && region->match(x[i][0],x[i][1],x[i][2])) {
           heat = vheat[i]*nevery*update->dt*force->ftm2v;
           vscale[i] =
             (ke + heat - 0.5*vcmsq*masstotal)/(ke - 0.5*vcmsq*masstotal);
           if (vscale[i] < 0.0)
             error->all(FLERR,
                        "Fix heat kinetic energy of an atom went negative");
           scale = sqrt(vscale[i]);
           if (rmass) massone = rmass[i];
           else massone = mass[type[i]];
           vsub[0] += (scale-1.0) * v[i][0]*massone;
           vsub[1] += (scale-1.0) * v[i][1]*massone;
           vsub[2] += (scale-1.0) * v[i][2]*massone;
         }
       }
 
       vsub[0] /= masstotal;
       vsub[1] /= masstotal;
       vsub[2] /= masstotal;
 
       for (i = 0; i < nlocal; i++)
         if (mask[i] & groupbit && region->match(x[i][0],x[i][1],x[i][2])) {
           scale = sqrt(vscale[i]);
           v[i][0] = scale*v[i][0] - vsub[0];
           v[i][1] = scale*v[i][1] - vsub[1];
           v[i][2] = scale*v[i][2] - vsub[2];
         }
     }
   }
 }
 
 /* ---------------------------------------------------------------------- */
 
 double FixHeat::compute_scalar()
 {
   double average_scale = scale;
   if (hstyle == ATOM) {
     double scale_sum = 0.0;
     int ncount = 0;
     int *mask = atom->mask;
     double **x = atom->x;
     int nlocal = atom->nlocal;
     if (iregion < 0) {
       for (int i = 0; i < nlocal; i++) {
         if (mask[i] & groupbit) {
           scale_sum += sqrt(vscale[i]);
           ncount++;
         }
       }
     } else {
       Region *region = domain->regions[iregion];
       region->prematch();
       for (int i = 0; i < nlocal; i++) {
         if (mask[i] & groupbit && region->match(x[i][0],x[i][1],x[i][2])) {
           scale_sum += sqrt(vscale[i]);
           ncount++;
         }
       }
     }
     double scale_sum_all = 0.0;
     int ncount_all = 0;
     MPI_Allreduce(&scale_sum,&scale_sum_all,1,MPI_DOUBLE,MPI_SUM,world);
     MPI_Allreduce(&ncount,&ncount_all,1,MPI_INT,MPI_SUM,world);
     if (ncount_all == 0) average_scale = 0.0;
     else average_scale = scale_sum_all/static_cast<double>(ncount_all);
   }
   return average_scale;
 }
 
 /* ----------------------------------------------------------------------
    memory usage of local atom-based arrays
 ------------------------------------------------------------------------- */
 
 double FixHeat::memory_usage()
 {
   double bytes = 0.0;
   if (hstyle == ATOM) bytes = atom->nmax*2 * sizeof(double);
   return bytes;
 }