diff --git a/src/charset.cpp b/src/charset.cpp
index 05ca1e62..9e91a1d3 100644
--- a/src/charset.cpp
+++ b/src/charset.cpp
@@ -44,24 +44,24 @@ std::locale internalLocale()
 	return loc;
 }
 
-std::string toUtf8From(std::string s, const char *charset)
+std::string toUtf8From(const std::string &s, const char *charset)
 {
 	return boost::locale::conv::to_utf<char>(s, charset);
 }
 
-std::string fromUtf8To(std::string s, const char *charset)
+std::string fromUtf8To(const std::string &s, const char *charset)
 {
 	return boost::locale::conv::to_utf<char>(s, charset);
 }
 
-std::string utf8ToLocale(std::string s)
+std::string utf8ToLocale(const std::string &s)
 {
 	return Config.system_encoding.empty()
 	     ? s
 	     : boost::locale::conv::from_utf<char>(s, Config.system_encoding);
 }
 
-std::string localeToUtf8(std::string s)
+std::string localeToUtf8(const std::string &s)
 {
 	return Config.system_encoding.empty()
 	     ? s
diff --git a/src/charset.h b/src/charset.h
index b28aae3d..2b335663 100644
--- a/src/charset.h
+++ b/src/charset.h
@@ -28,11 +28,11 @@ namespace Charset {
 
 std::locale internalLocale();
 
-std::string toUtf8From(std::string s, const char *charset);
-std::string fromUtf8To(std::string s, const char *charset);
+std::string toUtf8From(const std::string &s, const char *charset);
+std::string fromUtf8To(const std::string &s, const char *charset);
 
-std::string utf8ToLocale(std::string s);
-std::string localeToUtf8(std::string s);
+std::string utf8ToLocale(const std::string &s);
+std::string localeToUtf8(const std::string &s);
 
 }