diff --git a/src/fix_ave_chunk.cpp b/src/fix_ave_chunk.cpp
index 0ebdddb9df..2987783b2a 100644
--- a/src/fix_ave_chunk.cpp
+++ b/src/fix_ave_chunk.cpp
@@ -27,6 +27,8 @@
 #include "variable.h"
 #include "memory.h"
 #include "error.h"
+#include "utils.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -223,11 +225,9 @@ FixAveChunk::FixAveChunk(LAMMPS *lmp, int narg, char **arg) :
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/chunk command");
       if (me == 0) {
         fp = fopen(arg[iarg+1],"w");
-        if (fp == NULL) {
-          char str[128];
-          snprintf(str,128,"Cannot open fix ave/chunk file %s",arg[iarg+1]);
-          error->one(FLERR,str);
-        }
+        if (fp == NULL)
+          error->one(FLERR,fmt::format("Cannot open fix ave/chunk file {}: {}",
+                                       arg[iarg+1], utils::getsyserror()));
       }
       iarg += 2;
     } else if (strcmp(arg[iarg],"overwrite") == 0) {
diff --git a/src/fix_ave_correlate.cpp b/src/fix_ave_correlate.cpp
index 0a8a4cd17f..2231611d1e 100644
--- a/src/fix_ave_correlate.cpp
+++ b/src/fix_ave_correlate.cpp
@@ -30,6 +30,8 @@
 #include "memory.h"
 #include "error.h"
 #include "force.h"
+#include "utils.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -148,11 +150,9 @@ FixAveCorrelate::FixAveCorrelate(LAMMPS * lmp, int narg, char **arg):
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/correlate command");
       if (me == 0) {
         fp = fopen(arg[iarg+1],"w");
-        if (fp == NULL) {
-          char str[128];
-          snprintf(str,128,"Cannot open fix ave/correlate file %s",arg[iarg+1]);
-          error->one(FLERR,str);
-        }
+        if (fp == NULL)
+          error->one(FLERR,fmt::format("Cannot open fix ave/correlate file {}:"" {}",
+                                       arg[iarg+1], utils::getsyserror()));
       }
       iarg += 2;
     } else if (strcmp(arg[iarg],"overwrite") == 0) {
diff --git a/src/fix_ave_histo.cpp b/src/fix_ave_histo.cpp
index 1a292bf8d2..d0bedba34a 100644
--- a/src/fix_ave_histo.cpp
+++ b/src/fix_ave_histo.cpp
@@ -25,6 +25,8 @@
 #include "memory.h"
 #include "error.h"
 #include "force.h"
+#include "utils.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -963,11 +965,9 @@ void FixAveHisto::options(int iarg, int narg, char **arg)
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/histo command");
       if (me == 0) {
         fp = fopen(arg[iarg+1],"w");
-        if (fp == NULL) {
-          char str[128];
-          snprintf(str,128,"Cannot open fix ave/histo file %s",arg[iarg+1]);
-          error->one(FLERR,str);
-        }
+        if (fp == NULL)
+          error->one(FLERR,fmt::format("Cannot open fix ave/histo file {}: {}",
+                                       arg[iarg+1], utils::getsyserror()));
       }
       iarg += 2;
     } else if (strcmp(arg[iarg],"kind") == 0) {
diff --git a/src/fix_ave_time.cpp b/src/fix_ave_time.cpp
index 9b8dd13f05..84c5c04f11 100644
--- a/src/fix_ave_time.cpp
+++ b/src/fix_ave_time.cpp
@@ -28,6 +28,8 @@
 #include "variable.h"
 #include "memory.h"
 #include "error.h"
+#include "utils.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -1043,11 +1045,9 @@ void FixAveTime::options(int iarg, int narg, char **arg)
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
       if (me == 0) {
         fp = fopen(arg[iarg+1],"w");
-        if (fp == NULL) {
-          char str[128];
-          snprintf(str,128,"Cannot open fix ave/time file %s",arg[iarg+1]);
-          error->one(FLERR,str);
-        }
+        if (fp == NULL)
+          error->one(FLERR,fmt::format("Cannot open fix ave/time file {}: {}",
+                                       arg[iarg+1], utils::getsyserror()));
       }
       iarg += 2;
     } else if (strcmp(arg[iarg],"ave") == 0) {
diff --git a/src/fix_enforce2d.cpp b/src/fix_enforce2d.cpp
index 3edd24e9af..7dd8c08204 100644
--- a/src/fix_enforce2d.cpp
+++ b/src/fix_enforce2d.cpp
@@ -19,6 +19,7 @@
 #include "modify.h"
 #include "respa.h"
 #include "error.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -76,11 +77,9 @@ void FixEnforce2D::init()
       if (modify->fix[i]->enforce2d_flag) {
         if (myindex < 0)
           flist[nfixlist++] = modify->fix[i];
-        else {
-          char msg[256];
-          snprintf(msg,256,"Fix enforce2d must be defined after fix %s",modify->fix[i]->style);
-          error->all(FLERR,msg);
-        }
+        else
+          error->all(FLERR,fmt::format("Fix enforce2d must be defined after fix {}",
+                                       modify->fix[i]->style));
       }
       if (modify->fix[i] == this) myindex = i;
     }
diff --git a/src/fix_print.cpp b/src/fix_print.cpp
index 54a706d24b..8a988c8dac 100644
--- a/src/fix_print.cpp
+++ b/src/fix_print.cpp
@@ -21,6 +21,8 @@
 #include "memory.h"
 #include "error.h"
 #include "force.h"
+#include "utils.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -65,11 +67,9 @@ FixPrint::FixPrint(LAMMPS *lmp, int narg, char **arg) :
       if (me == 0) {
         if (strcmp(arg[iarg],"file") == 0) fp = fopen(arg[iarg+1],"w");
         else fp = fopen(arg[iarg+1],"a");
-        if (fp == NULL) {
-          char str[128];
-          snprintf(str,128,"Cannot open fix print file %s",arg[iarg+1]);
-          error->one(FLERR,str);
-        }
+        if (fp == NULL)
+          error->one(FLERR,fmt::format("Cannot open fix print file {}: {}",
+                                       arg[iarg+1], utils::getsyserror()));
       }
       iarg += 2;
     } else if (strcmp(arg[iarg],"screen") == 0) {
diff --git a/src/fix_property_atom.cpp b/src/fix_property_atom.cpp
index 5fb17ca636..aeea9a7dca 100644
--- a/src/fix_property_atom.cpp
+++ b/src/fix_property_atom.cpp
@@ -19,6 +19,7 @@
 #include "memory.h"
 #include "error.h"
 #include "utils.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -221,11 +222,8 @@ void FixPropertyAtom::read_data_section(char *keyword, int n, char *buf,
   int nwords = utils::count_words(buf);
   *next = '\n';
 
-  if (nwords != nvalue+1) {
-    char str[128];
-    snprintf(str,128,"Incorrect %s format in data file",keyword);
-    error->all(FLERR,str);
-  }
+  if (nwords != nvalue+1)
+    error->all(FLERR,fmt::format("Incorrect {} format in data file",keyword));
 
   char **values = new char*[nwords];
 
@@ -239,28 +237,21 @@ void FixPropertyAtom::read_data_section(char *keyword, int n, char *buf,
     next = strchr(buf,'\n');
 
     values[0] = strtok(buf," \t\n\r\f");
-    if (values[0] == NULL) {
-      char str[128];
-      snprintf(str,128,"Too few lines in %s section of data file",keyword);
-      error->one(FLERR,str);
-    }
+    if (values[0] == NULL)
+      error->all(FLERR,fmt::format("Too few lines in {} section of data file",keyword));
+
     int format_ok = 1;
     for (j = 1; j < nwords; j++) {
       values[j] = strtok(NULL," \t\n\r\f");
       if (values[j] == NULL) format_ok = 0;
     }
-    if (!format_ok) {
-      char str[128];
-      snprintf(str,128,"Incorrect %s format in data file",keyword);
-      error->all(FLERR,str);
-    }
+    if (!format_ok)
+      error->all(FLERR,fmt::format("Incorrect {} format in data file",keyword));
 
     itag = ATOTAGINT(values[0]) + id_offset;
-    if (itag <= 0 || itag > map_tag_max) {
-      char str[128];
-      snprintf(str,128,"Invalid atom ID in %s section of data file",keyword);
-      error->one(FLERR,str);
-    }
+    if (itag <= 0 || itag > map_tag_max)
+      error->all(FLERR,fmt::format("Invalid atom ID {} in {} section of "
+                                   "data file",itag, keyword));
 
     // assign words in line to per-atom vectors
 
diff --git a/src/fix_tmd.cpp b/src/fix_tmd.cpp
index 182da8ecaa..a174c2efa4 100644
--- a/src/fix_tmd.cpp
+++ b/src/fix_tmd.cpp
@@ -30,6 +30,7 @@
 #include "memory.h"
 #include "error.h"
 #include "utils.h"
+#include "fmt/format.h"
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -73,11 +74,9 @@ nfileevery(0), fp(NULL), xf(NULL), xold(NULL)
     if (narg != 7) error->all(FLERR,"Illegal fix tmd command");
     if (me == 0) {
       fp = fopen(arg[6],"w");
-      if (fp == NULL) {
-        char str[128];
-        snprintf(str,128,"Cannot open fix tmd file %s",arg[6]);
-        error->one(FLERR,str);
-      }
+      if (fp == NULL)
+        error->one(FLERR,fmt::format("Cannot open fix tmd file {}: {}",
+                                     arg[6], utils::getsyserror()));
       fprintf(fp,"%s %s\n","# Step rho_target rho_old gamma_back",
               "gamma_forward lambda work_lambda work_analytical");
     }