diff --git a/src/ADIOS/dump_custom_adios.cpp b/src/ADIOS/dump_custom_adios.cpp
index 211a550f5e..305f3d3032 100644
--- a/src/ADIOS/dump_custom_adios.cpp
+++ b/src/ADIOS/dump_custom_adios.cpp
@@ -219,7 +219,7 @@ void DumpCustomADIOS::init_style()
   delete[] columns;
   std::string combined;
   int icol = 0;
-  for (auto item : utils::split_words(columns_default)) {
+  for (const auto &item : utils::split_words(columns_default)) {
     if (combined.size()) combined += " ";
     if (keyword_user[icol].size())
       combined += keyword_user[icol];
diff --git a/src/MPIIO/dump_atom_mpiio.cpp b/src/MPIIO/dump_atom_mpiio.cpp
index c275b387db..87ef2b0342 100644
--- a/src/MPIIO/dump_atom_mpiio.cpp
+++ b/src/MPIIO/dump_atom_mpiio.cpp
@@ -236,7 +236,7 @@ void DumpAtomMPIIO::init_style()
 
   int icol = 0;
   columns.clear();
-  for (auto item : utils::split_words(default_columns)) {
+  for (const auto &item : utils::split_words(default_columns)) {
     if (columns.size()) columns += " ";
     if (keyword_user[icol].size())
       columns += keyword_user[icol];
diff --git a/src/MPIIO/dump_custom_mpiio.cpp b/src/MPIIO/dump_custom_mpiio.cpp
index 678ee3dadd..a5b2a681d3 100644
--- a/src/MPIIO/dump_custom_mpiio.cpp
+++ b/src/MPIIO/dump_custom_mpiio.cpp
@@ -207,7 +207,7 @@ void DumpCustomMPIIO::init_style()
   delete[] columns;
   std::string combined;
   int icol = 0;
-  for (auto item : utils::split_words(columns_default)) {
+  for (const auto &item : utils::split_words(columns_default)) {
     if (combined.size()) combined += " ";
     if (keyword_user[icol].size())
       combined += keyword_user[icol];
diff --git a/src/PLUGIN/plugin.cpp b/src/PLUGIN/plugin.cpp
index 6b11ac269f..5451cd31e2 100644
--- a/src/PLUGIN/plugin.cpp
+++ b/src/PLUGIN/plugin.cpp
@@ -448,7 +448,7 @@ int plugin_get_num_plugins()
 int plugin_find(const char *style, const char *name)
 {
   int i = 0;
-  for (auto entry : pluginlist) {
+  for (const auto &entry : pluginlist) {
     if ((strcmp(style, entry.style) == 0) && (strcmp(name, entry.name) == 0)) return i;
     ++i;
   }
diff --git a/src/dump.cpp b/src/dump.cpp
index 51dae8b131..247da8595a 100644
--- a/src/dump.cpp
+++ b/src/dump.cpp
@@ -1136,7 +1136,7 @@ void Dump::modify_params(int narg, char **arg)
     } else if (strcmp(arg[iarg],"colname") == 0) {
       if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "dump_modify colname", error);
       if (strcmp(arg[iarg+1],"default") == 0) {
-        for (auto item : keyword_user) item.clear();
+        for (auto &item : keyword_user) item.clear();
         iarg += 2;
       } else {
         if (iarg+3 > narg) utils::missing_cmd_args(FLERR, "dump_modify colname", error);
diff --git a/src/dump_atom.cpp b/src/dump_atom.cpp
index f52ba94f33..ef567abdb2 100644
--- a/src/dump_atom.cpp
+++ b/src/dump_atom.cpp
@@ -80,7 +80,7 @@ void DumpAtom::init_style()
 
   int icol = 0;
   columns.clear();
-  for (auto item : utils::split_words(default_columns)) {
+  for (const auto &item : utils::split_words(default_columns)) {
     if (columns.size()) columns += " ";
     if (keyword_user[icol].size()) columns += keyword_user[icol];
     else columns += item;
diff --git a/src/dump_custom.cpp b/src/dump_custom.cpp
index 1e7ad367ec..2417a05c2c 100644
--- a/src/dump_custom.cpp
+++ b/src/dump_custom.cpp
@@ -241,7 +241,7 @@ void DumpCustom::init_style()
   delete[] columns;
   std::string combined;
   int icol = 0;
-  for (auto item : utils::split_words(columns_default)) {
+  for (const auto &item : utils::split_words(columns_default)) {
     if (combined.size()) combined += " ";
     if (keyword_user[icol].size()) combined += keyword_user[icol];
     else combined += item;
diff --git a/src/dump_local.cpp b/src/dump_local.cpp
index bf26890b05..b7a390a749 100644
--- a/src/dump_local.cpp
+++ b/src/dump_local.cpp
@@ -161,7 +161,7 @@ void DumpLocal::init_style()
   delete[] columns;
   std::string combined;
   int icol = 0;
-  for (auto item : utils::split_words(columns_default)) {
+  for (const auto &item : utils::split_words(columns_default)) {
     if (combined.size()) combined += " ";
     if (keyword_user[icol].size()) combined += keyword_user[icol];
     else combined += item;
diff --git a/src/fix_ave_time.cpp b/src/fix_ave_time.cpp
index 010170e149..1a437783e7 100644
--- a/src/fix_ave_time.cpp
+++ b/src/fix_ave_time.cpp
@@ -678,7 +678,7 @@ void FixAveTime::invoke_scalar(bigint ntimestep)
       if (!yaml_header || overwrite) {
         yaml_header = true;
         fputs("keywords: ['Step', ", fp);
-        for (auto k : keyword) fmt::print(fp, "'{}', ", k);
+        for (const auto &k : keyword) fmt::print(fp, "'{}', ", k);
         fputs("]\ndata:\n", fp);
       }
       fmt::print(fp, "  - [{}, ", ntimestep);
@@ -900,7 +900,7 @@ void FixAveTime::invoke_vector(bigint ntimestep)
       if (!yaml_header || overwrite) {
         yaml_header = true;
         fputs("keywords: [", fp);
-        for (auto k : keyword) fmt::print(fp, "'{}', ", k);
+        for (const auto &k : keyword) fmt::print(fp, "'{}', ", k);
         fputs("]\ndata:\n", fp);
       }
       fmt::print(fp, "  {}:\n", ntimestep);
diff --git a/src/thermo.cpp b/src/thermo.cpp
index c4a914e3a3..518deab618 100644
--- a/src/thermo.cpp
+++ b/src/thermo.cpp
@@ -629,7 +629,7 @@ void Thermo::modify_params(int narg, char **arg)
     } else if (strcmp(arg[iarg], "colname") == 0) {
       if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "thermo_modify colname", error);
       if (strcmp(arg[iarg + 1], "default") == 0) {
-        for (auto item : keyword_user) item.clear();
+        for (auto &item : keyword_user) item.clear();
         iarg += 2;
       } else {
         if (iarg + 3 > narg) utils::missing_cmd_args(FLERR, "thermo_modify colname", error);
@@ -658,7 +658,7 @@ void Thermo::modify_params(int narg, char **arg)
         format_int_user.clear();
         format_bigint_user.clear();
         format_float_user.clear();
-        for (auto item : format_column_user) item.clear();
+        for (auto &item : format_column_user) item.clear();
         iarg += 2;
         continue;
       }
@@ -747,7 +747,7 @@ void Thermo::allocate()
 
   int i = 0;
   key2col.clear();
-  for (auto item : utils::split_words(line)) { key2col[item] = i++; }
+  for (const auto &item : utils::split_words(line)) { key2col[item] = i++; }
 }
 
 /* ----------------------------------------------------------------------