diff --git a/src/text_file_reader.cpp b/src/text_file_reader.cpp
index 8fc57d9283..ab1c81efb1 100644
--- a/src/text_file_reader.cpp
+++ b/src/text_file_reader.cpp
@@ -22,6 +22,7 @@
 #include "utils.h"
 
 #include <cstring>
+#include <utility>
 
 using namespace LAMMPS_NS;
 
@@ -68,8 +69,8 @@ This function is useful in combination with :cpp:func:`utils::open_potential`.
  * \param  fp        File descriptor of the already opened file
  * \param  filetype  Description of file type for error messages */
 
-TextFileReader::TextFileReader(FILE *fp, const std::string &filetype) :
-    filetype(filetype), closefp(false), fp(fp), ignore_comments(true)
+TextFileReader::TextFileReader(FILE *fp, std::string filetype) :
+    filetype(std::move(filetype)), closefp(false), fp(fp), ignore_comments(true)
 {
   if (fp == nullptr) throw FileReaderException("Invalid file descriptor");
 }
diff --git a/src/text_file_reader.h b/src/text_file_reader.h
index 826f470299..34556d7eb3 100644
--- a/src/text_file_reader.h
+++ b/src/text_file_reader.h
@@ -34,7 +34,7 @@ class TextFileReader {
   bool ignore_comments;    //!< Controls whether comments are ignored
 
   TextFileReader(const std::string &filename, const std::string &filetype);
-  TextFileReader(FILE *fp, const std::string &filetype);
+  TextFileReader(FILE *fp, std::string filetype);
 
   ~TextFileReader();
 
diff --git a/src/tokenizer.cpp b/src/tokenizer.cpp
index 95aa175fdf..35a313ab3d 100644
--- a/src/tokenizer.cpp
+++ b/src/tokenizer.cpp
@@ -49,8 +49,8 @@ TokenizerException::TokenizerException(const std::string &msg, const std::string
  * \param  str          string to be processed
  * \param  _separators  string with separator characters (default: " \t\r\n\f") */
 
-Tokenizer::Tokenizer(const std::string &str, const std::string &_separators) :
-    text(str), separators(_separators), start(0), ntokens(std::string::npos)
+Tokenizer::Tokenizer(std::string str, std::string _separators) :
+    text(std::move(str)), separators(std::move(_separators)), start(0), ntokens(std::string::npos)
 {
     // replace known UTF-8 characters with ASCII equivalents
     if (utils::has_utf8(text)) text = utils::utf8_subst(text);
diff --git a/src/tokenizer.h b/src/tokenizer.h
index cacfc541a4..247afd0240 100644
--- a/src/tokenizer.h
+++ b/src/tokenizer.h
@@ -35,7 +35,7 @@ class Tokenizer {
   size_t ntokens;
 
  public:
-  Tokenizer(const std::string &str, const std::string &separators = TOKENIZER_DEFAULT_SEPARATORS);
+  Tokenizer(std::string str, std::string separators = TOKENIZER_DEFAULT_SEPARATORS);
   Tokenizer(Tokenizer &&);
   Tokenizer(const Tokenizer &);
   Tokenizer &operator=(const Tokenizer &);