2 files changed, 9 insertions, 5 deletions
diff --git a/src/util.cc b/src/util.cc
index 6fc650a..9052118 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -7,12 +7,16 @@
 #include <fstream>
 #include <algorithm>
 #include <sstream>
+#include <cctype>
 
-std::string to_lower(const std::string& str)
+std::string to_lower(std::string str)
 {
-	std::string out{str};
-	std::transform(out.begin(), out.end(), out.begin(), ::tolower);
-	return out;
+	std::transform(str.begin(), str.end(), str.begin(),
+	               [](unsigned char c)
+	               {
+		               return std::tolower(c);
+	               });
+	return str;
 }
 
 std::string readFile(const std::string& fileName)
diff --git a/src/util.h b/src/util.h
index 8b41014..6e1bc7b 100644
--- a/src/util.h
+++ b/src/util.h
@@ -9,7 +9,7 @@
 #include <filesystem>
 #include <cstdlib>
 
-std::string to_lower(const std::string& str);
+std::string to_lower(std::string str);
 
 std::string readFile(const std::string& fileName);
 ctor::language languageFromExtension(const std::filesystem::path& file);