diff --git a/src/REPLICA/neb.cpp b/src/REPLICA/neb.cpp
index f021a1f7fa..6e7b54660a 100644
--- a/src/REPLICA/neb.cpp
+++ b/src/REPLICA/neb.cpp
@@ -192,6 +192,8 @@ void NEB::run()
   update->endstep = update->laststep = update->firststep + n1steps;
   update->nsteps = n1steps;
   update->max_eval = n1steps;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many timesteps");
 
   update->minimize->setup();
   
@@ -259,6 +261,8 @@ void NEB::run()
   update->endstep = update->laststep = update->firststep + n2steps;
   update->nsteps = n2steps;
   update->max_eval = n2steps;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many timesteps");
 
   update->minimize->init();
   fneb->rclimber = top;
diff --git a/src/REPLICA/prd.cpp b/src/REPLICA/prd.cpp
index 07ca60580e..95ebf5e9cb 100644
--- a/src/REPLICA/prd.cpp
+++ b/src/REPLICA/prd.cpp
@@ -210,6 +210,8 @@ void PRD::command(int narg, char **arg)
   update->beginstep = update->firststep = update->ntimestep;
   update->endstep = update->laststep = update->firststep + nsteps;
   update->restrict_output = 1;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many timesteps");
 
   lmp->init();
 
@@ -495,6 +497,8 @@ void PRD::quench()
   update->whichflag = 2;
   update->nsteps = maxiter;
   update->endstep = update->laststep = update->firststep + maxiter;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many iterations");
 
   // full init works
 
diff --git a/src/REPLICA/tad.cpp b/src/REPLICA/tad.cpp
index 0cbb937075..ad4602696f 100644
--- a/src/REPLICA/tad.cpp
+++ b/src/REPLICA/tad.cpp
@@ -195,6 +195,8 @@ void TAD::command(int narg, char **arg)
   update->beginstep = update->firststep = update->ntimestep;
   update->endstep = update->laststep = update->firststep + nsteps;
   update->restrict_output = 1;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many timesteps");
 
   lmp->init();
 
@@ -460,6 +462,8 @@ void TAD::quench()
   update->whichflag = 2;
   update->nsteps = maxiter;
   update->endstep = update->laststep = update->firststep + maxiter;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many iterations");
 
   // full init works
 
diff --git a/src/REPLICA/temper.cpp b/src/REPLICA/temper.cpp
index 17fcc41c76..4befb443b3 100644
--- a/src/REPLICA/temper.cpp
+++ b/src/REPLICA/temper.cpp
@@ -106,6 +106,8 @@ void Temper::command(int narg, char **arg)
   update->nsteps = nsteps;
   update->beginstep = update->firststep = update->ntimestep;
   update->endstep = update->laststep = update->firststep + nsteps;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many timesteps");
 
   lmp->init();
 
diff --git a/src/fix_dt_reset.h b/src/fix_dt_reset.h
index 7105dc442b..ddba09c73d 100644
--- a/src/fix_dt_reset.h
+++ b/src/fix_dt_reset.h
@@ -21,6 +21,7 @@ FixStyle(dt/reset,FixDtReset)
 #define LMP_FIX_DT_RESET_H
 
 #include "fix.h"
+#include "lmptype.h"
 
 namespace LAMMPS_NS {
 
@@ -36,7 +37,8 @@ class FixDtReset : public Fix {
   double compute_vector(int);
 
  private:
-  int minbound,maxbound,laststep;
+  bigint laststep;
+  int minbound,maxbound;
   double tmin,tmax,xmax;
   double ftm2v;
   double t_elapsed;
diff --git a/src/lmptype.h b/src/lmptype.h
index 84c135e248..6d45da2709 100644
--- a/src/lmptype.h
+++ b/src/lmptype.h
@@ -13,7 +13,7 @@
 
 // define integer data types used by LAMMPS and associated size limits
 
-// smallint = variables for system on 1 processor (nlocal, etc)
+// smallint = variables for system on 1 processor (nlocal, nmax, etc)
 // tagint = variables for atom IDs (tag)
 // bigint = variables for total system (natoms, ntimestep, etc)
 
@@ -31,8 +31,8 @@
 
 // NOTE: if your machine/MPI does not support "long long" ints,
 //       but only "long" ints, then you will likely need to set
-//       MPI_LMP_BIGINT to MPI_LONG, LLONG_MAX to LONG_MAX,
-//       "lld" to "ld", and ATOBIGINT to atol
+//       MPI_LONG_LONG to MPI_LONG, LLONG_MAX to LONG_MAX,
+//       "lld" to "ld", and atoll to atol
 
 #ifndef LMP_LMPTYPE_H
 #define LMP_LMPTYPE_H
diff --git a/src/minimize.cpp b/src/minimize.cpp
index 94d748f9dd..3d308b9de8 100644
--- a/src/minimize.cpp
+++ b/src/minimize.cpp
@@ -46,6 +46,8 @@ void Minimize::command(int narg, char **arg)
   update->whichflag = 2;
   update->beginstep = update->firststep = update->ntimestep;
   update->endstep = update->laststep = update->firststep + update->nsteps;
+  if (update->laststep < 0 || update->laststep > MAXBIGINT)
+    error->all("Too many iterations");
 
   lmp->init();
   update->minimize->setup();
diff --git a/src/run.cpp b/src/run.cpp
index 63de1ec2a3..e5a1b318ea 100644
--- a/src/run.cpp
+++ b/src/run.cpp
@@ -14,6 +14,7 @@
 #include "stdlib.h"
 #include "string.h"
 #include "run.h"
+#include "lmptype.h"
 #include "domain.h"
 #include "update.h"
 #include "integrate.h"
@@ -44,14 +45,14 @@ void Run::command(int narg, char **arg)
   if (domain->box_exist == 0)
     error->all("Run command before simulation box is defined");
 
-  int nsteps = atoi(arg[0]);
+  bigint nsteps_input = ATOBIGINT(arg[0]);
 
   // parse optional args
 
   int uptoflag = 0;
   int startflag = 0;
   int stopflag = 0;
-  int start,stop;
+  bigint start,stop;
   int preflag = 1;
   int postflag = 1;
   int nevery = 0;
@@ -67,12 +68,12 @@ void Run::command(int narg, char **arg)
     } else if (strcmp(arg[iarg],"start") == 0) {
       if (iarg+2 > narg) error->all("Illegal run command");
       startflag = 1;
-      start = atoi(arg[iarg+1]);
+      start = ATOBIGINT(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"stop") == 0) {
       if (iarg+2 > narg) error->all("Illegal run command");
       stopflag = 1;
-      stop = atoi(arg[iarg+1]);
+      stop = ATOBIGINT(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"pre") == 0) {
       if (iarg+2 > narg) error->all("Illegal run command");
@@ -103,9 +104,34 @@ void Run::command(int narg, char **arg)
     } else error->all("Illegal run command");
   }
 
-  // adjust nsteps if upto was specified
+  // set nsteps as integer, using upto value if specified
+  
+  int nsteps;
+  if (!uptoflag) {
+    if (nsteps_input < 0 || nsteps_input > MAXSMALLINT)
+      error->all("Invalid run command N value");
+    nsteps = static_cast<int> (nsteps_input);
+  } else {
+    bigint delta = nsteps_input - update->ntimestep;
+    if (delta < 0 || delta > MAXSMALLINT)
+      error->all("Invalid run command upto value");
+    nsteps = static_cast<int> (delta);
+  }
 
-  if (uptoflag) nsteps -= update->ntimestep;
+  // error check
+
+  if (startflag) {
+    if (start < 0 || start > MAXBIGINT)
+      error->all("Invalid run command start/stop value");
+    if (start > update->ntimestep)
+      error->all("Run command start value is after start of run");
+  }
+  if (stopflag) {
+    if (stop < 0 || stop > MAXBIGINT)
+      error->all("Invalid run command start/stop value");
+    if (stop < update->ntimestep + nsteps)
+      error->all("Run command stop value is before end of run");
+  }
 
   // if nevery, make copies of arg strings that are commands
   // required because re-parsing commands via input->one() will wipe out args
@@ -122,15 +148,6 @@ void Run::command(int narg, char **arg)
     }
   }
 
-  // error check
-
-  if (uptoflag && nsteps < 0)
-    error->all("Run command upto value is before current timestep");
-  if (startflag && start > update->ntimestep)
-    error->all("Run command start value is after start of run");
-  if (stopflag && stop < update->ntimestep + nsteps)
-    error->all("Run command stop value is before end of run");
-
   // perform a single run
   // use start/stop to set begin/end step
   // if pre or 1st run, do System init/setup,
@@ -143,6 +160,8 @@ void Run::command(int narg, char **arg)
     update->nsteps = nsteps;
     update->firststep = update->ntimestep;
     update->laststep = update->ntimestep + nsteps;
+    if (update->laststep < 0 || update->laststep > MAXBIGINT)
+      error->all("Too many timesteps");
 
     if (startflag) update->beginstep = start;
     else update->beginstep = update->firststep;
@@ -181,6 +200,8 @@ void Run::command(int narg, char **arg)
       update->nsteps = nsteps;
       update->firststep = update->ntimestep;
       update->laststep = update->ntimestep + nsteps;
+      if (update->laststep < 0 || update->laststep > MAXBIGINT)
+	error->all("Too many timesteps");
 
       if (startflag) update->beginstep = start;
       else update->beginstep = update->firststep;