diff --git a/src/utils.cpp b/src/utils.cpp
index 4efa35a8d1..7e1229dc0f 100644
--- a/src/utils.cpp
+++ b/src/utils.cpp
@@ -82,7 +82,7 @@ using namespace LAMMPS_NS;
  *  even with char * type variables.
  *  Example: utils::strmatch(text, std::string("^") + charptr)
  */
-bool utils::strmatch(std::string text, std::string pattern)
+bool utils::strmatch(const std::string &text, const std::string &pattern)
 {
   const int pos = re_match(text.c_str(),pattern.c_str());
   return (pos >= 0);
diff --git a/src/utils.h b/src/utils.h
index abaa87ca5f..91001c0fb0 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -35,7 +35,7 @@ namespace LAMMPS_NS {
      *  \param pattern the search pattern, which may contain regexp markers
      *  \return true if the pattern matches, false if not
      */
-    bool strmatch(std::string text, std::string pattern);
+    bool strmatch(const std::string &text, const std::string &pattern);
 
     /** \brief Send message to screen and logfile, if available
      *
@@ -148,7 +148,7 @@ namespace LAMMPS_NS {
      * \param line string that should be trimmed
      * \return new string without comment (string)
      */
-    std::string trim_comment(const std::string & line);
+    std::string trim_comment(const std::string &line);
 
     /**
      * \brief Count words in string