diff --git a/include/util.hpp b/include/util.hpp
index ba91709..f3e20dd 100644
--- a/include/util.hpp
+++ b/include/util.hpp
@@ -66,8 +66,8 @@ std::string  which(const std::string& command);
 bool         read_binary_file(std::ifstream& f, std::string& ret);
 void         replace_str(std::string& str, const std::string_view from, const std::string_view to);
 bool         read_exec(std::vector<const char*> cmd, std::string& output, bool useStdErr = false, bool noerror_print = true);
-std::string  str_tolower(std::string_view str);
-std::string  str_toupper(std::string_view str);
+std::string  str_tolower(std::string str);
+std::string  str_toupper(std::string str);
 void         strip(std::string& input);
 std::string  read_by_syspath(const std::string_view path);
 fmt::rgb     hexStringToColor(const std::string_view hexstr);
diff --git a/src/util.cpp b/src/util.cpp
index 7d74f67..725baa8 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -350,20 +350,20 @@ bool read_exec(std::vector<const char*> cmd, std::string& output, bool useStdErr
     return false;
 }
 
-std::string str_tolower(std::string_view str)
+std::string str_tolower(std::string str)
 {
-    for (char x : str)
+    for (char& x : str)
         x = std::tolower(x);
 
-    return str.data();
+    return str;
 }
 
-std::string str_toupper(std::string_view str)
+std::string str_toupper(std::string str)
 {
-    for (char x : str)
+    for (char& x : str)
         x = std::toupper(x);
 
-    return str.data();
+    return str;
 }
 
 // Function to perform binary search on the pci vendors array to find a device from a vendor.