diff --git a/src/balance.cpp b/src/balance.cpp
index c8d21f1ac6..92321bcf84 100644
--- a/src/balance.cpp
+++ b/src/balance.cpp
@@ -196,8 +196,8 @@ void Balance::command(int narg, char **arg)
       if (style != -1) error->all(FLERR,"Illegal balance command");
       if (iarg+4 > narg) error->all(FLERR,"Illegal balance command");
       style = SHIFT;
-      if (strlen(arg[iarg+1]) > 3) error->all(FLERR,"Illegal balance command");
-      strcpy(bstr,arg[iarg+1]);
+      if (strlen(arg[iarg+1]) > BSTR_SIZE) error->all(FLERR,"Illegal balance command");
+      strncpy(bstr,arg[iarg+1],BSTR_SIZE);
       nitermax = utils::inumeric(FLERR,arg[iarg+2],false,lmp);
       if (nitermax <= 0) error->all(FLERR,"Illegal balance command");
       stopthresh = utils::numeric(FLERR,arg[iarg+3],false,lmp);
diff --git a/src/balance.h b/src/balance.h
index e427c8bd9b..2e3f003fbd 100644
--- a/src/balance.h
+++ b/src/balance.h
@@ -56,7 +56,8 @@ class Balance : public Command {
 
   int nitermax;    // params for shift LB
   double stopthresh;
-  char bstr[4];
+  static constexpr int BSTR_SIZE = 3;
+  char bstr[BSTR_SIZE+1];
 
   int shift_allocate;       // 1 if SHIFT vectors have been allocated
   int ndim;                 // length of balance string bstr