diff --git a/SystemInformation.cxx b/SystemInformation.cxx
index bfc895e945cb12699abd11bf20e0593fa77769e2..b7bd102714295642bbb56bd56ce7a1387bc95f3c 100644
--- a/SystemInformation.cxx
+++ b/SystemInformation.cxx
@@ -918,7 +918,8 @@ int LoadLines(const char* fileName, std::vector<std::string>& lines)
 
 // ****************************************************************************
 template <typename T>
-int NameValue(std::vector<std::string>& lines, std::string name, T& value)
+int NameValue(std::vector<std::string> const& lines, std::string const& name,
+              T& value)
 {
   size_t nLines = lines.size();
   for (size_t i = 0; i < nLines; ++i) {
diff --git a/testSystemTools.cxx b/testSystemTools.cxx
index 900894c518544adeb82b0117f3fcbd0c76280c46..e6fbf6cdafb8ae2197ac3b815ff8b3e5c6535b72 100644
--- a/testSystemTools.cxx
+++ b/testSystemTools.cxx
@@ -54,7 +54,8 @@ static const char* toUnixPaths[][2] = {
   { 0, 0 }
 };
 
-static bool CheckConvertToUnixSlashes(std::string input, std::string output)
+static bool CheckConvertToUnixSlashes(std::string const& input,
+                                      std::string const& output)
 {
   std::string result = input;
   kwsys::SystemTools::ConvertToUnixSlashes(result);
@@ -71,8 +72,9 @@ static const char* checkEscapeChars[][4] = { { "1 foo 2 bar 2", "12", "\\",
                                              { " {} ", "{}", "#", " #{#} " },
                                              { 0, 0, 0, 0 } };
 
-static bool CheckEscapeChars(std::string input, const char* chars_to_escape,
-                             char escape_char, std::string output)
+static bool CheckEscapeChars(std::string const& input,
+                             const char* chars_to_escape, char escape_char,
+                             std::string const& output)
 {
   std::string result = kwsys::SystemTools::EscapeChars(
     input.c_str(), chars_to_escape, escape_char);