diff --git a/src/KOKKOS/pair_reaxc_kokkos.cpp b/src/KOKKOS/pair_reaxc_kokkos.cpp
index 16d4b63928..64651be270 100644
--- a/src/KOKKOS/pair_reaxc_kokkos.cpp
+++ b/src/KOKKOS/pair_reaxc_kokkos.cpp
@@ -143,7 +143,7 @@ template<class DeviceType>
 void PairReaxCKokkos<DeviceType>::init_style()
 {
   PairReaxC::init_style();
-  if (fix_reax) modify->delete_fix(fix_id.c_str()); // not needed in the Kokkos version
+  if (fix_reax) modify->delete_fix(fix_id); // not needed in the Kokkos version
   fix_reax = NULL;
 
   // irequest = neigh request made by parent class
diff --git a/src/USER-OMP/pair_reaxc_omp.cpp b/src/USER-OMP/pair_reaxc_omp.cpp
index 28a4b6a30f..eb3e6c92a0 100644
--- a/src/USER-OMP/pair_reaxc_omp.cpp
+++ b/src/USER-OMP/pair_reaxc_omp.cpp
@@ -33,8 +33,6 @@
    High Performance Computing Applications, to appear.
  ------------------------------------------------------------------------- */
 
-#include <sstream>
-
 #include "pair_reaxc_omp.h"
 #include "atom.h"
 #include "update.h"
@@ -99,9 +97,7 @@ PairReaxCOMP::PairReaxCOMP(LAMMPS *lmp) : PairReaxC(lmp), ThrOMP(lmp, THR_PAIR)
 
   num_nbrs_offset = NULL;
 
-  std::stringstream ss;
-  ss << "REAXC_COMP_" << std::dec << Pair::instance_me;
-  fix_id = ss.str();
+  sprintf(fix_id, "REAXC_OMP_%d", Pair::instance_me);
 
 #ifdef OMP_TIMING
   for (int i=0;i<LASTTIMINGINDEX;i++) {
@@ -379,7 +375,7 @@ void PairReaxCOMP::init_style( )
 
   if (fix_reax == NULL) {
     char **fixarg = new char*[3];
-    fixarg[0] = (char *) fix_id.c_str();
+    fixarg[0] = (char *) fix_id;
     fixarg[1] = (char *) "all";
     fixarg[2] = (char *) "REAXC";
     modify->add_fix(3,fixarg);
diff --git a/src/USER-OMP/pair_reaxc_omp.h b/src/USER-OMP/pair_reaxc_omp.h
index a0dc20e985..b831f61f0b 100644
--- a/src/USER-OMP/pair_reaxc_omp.h
+++ b/src/USER-OMP/pair_reaxc_omp.h
@@ -76,7 +76,7 @@ class PairReaxCOMP : public PairReaxC, public ThrOMP {
   }
 
  protected:
-  std::string fix_id;
+  char fix_id[128];
   virtual void setup();
   virtual void write_reax_atoms();
   virtual int estimate_reax_lists();
diff --git a/src/USER-REAXC/pair_reaxc.cpp b/src/USER-REAXC/pair_reaxc.cpp
index 1b949d6983..f943715420 100644
--- a/src/USER-REAXC/pair_reaxc.cpp
+++ b/src/USER-REAXC/pair_reaxc.cpp
@@ -20,8 +20,6 @@
    Hybrid and hybrid/overlay compatibility added by Ray Shan (Sandia)
 ------------------------------------------------------------------------- */
 
-#include <sstream>
-
 #include "pair_reaxc.h"
 #include "atom.h"
 #include "update.h"
@@ -76,9 +74,7 @@ PairReaxC::PairReaxC(LAMMPS *lmp) : Pair(lmp)
   manybody_flag = 1;
   ghostneigh = 1;
 
-  std::stringstream ss;
-  ss << "REAXC_" << std::dec << Pair::instance_me;
-  fix_id = ss.str();
+  sprintf(fix_id, "REAXC_%d", Pair::instance_me);
 
   system = (reax_system *)
     memory->smalloc(sizeof(reax_system),"reax:system");
@@ -141,7 +137,7 @@ PairReaxC::~PairReaxC()
 {
   if (copymode) return;
 
-  if (fix_reax) modify->delete_fix(fix_id.c_str());
+  if (fix_reax) modify->delete_fix(fix_id);
 
   if (setup_flag) {
     Close_Output_Files( system, control, out_control, mpi_data );
@@ -418,7 +414,7 @@ void PairReaxC::init_style( )
 
   if (fix_reax == NULL) {
     char **fixarg = new char*[3];
-    fixarg[0] = (char *) fix_id.c_str();
+    fixarg[0] = (char *) fix_id;
     fixarg[1] = (char *) "all";
     fixarg[2] = (char *) "REAXC";
     modify->add_fix(3,fixarg);
diff --git a/src/USER-REAXC/pair_reaxc.h b/src/USER-REAXC/pair_reaxc.h
index 75cf7eb429..5f60abdb67 100644
--- a/src/USER-REAXC/pair_reaxc.h
+++ b/src/USER-REAXC/pair_reaxc.h
@@ -60,7 +60,7 @@ class PairReaxC : public Pair {
   bigint ngroup;
 
  protected:
-  std::string fix_id;
+  char fix_id[128];
   double cutmax;
   int nelements;                // # of unique elements
   char **elements;              // names of unique elements