diff --git a/hex_functions.cpp b/hex_functions.cpp
index e07a7b0..683097e 100644
--- a/hex_functions.cpp
+++ b/hex_functions.cpp
@@ -57,10 +57,10 @@ namespace omni
       return "FF";
 
     std::stringstream stream;
-    stream << std::setfill ('0') << std::setw(sizeof(char)*2) 
+    stream << std::setfill('0') << std::setw(sizeof(char)*2)
        << std::hex << input;
     std::string result(stream.str());
-    std::transform(str.begin(), str.end(), str.begin(), ::toupper);
+    std::transform(result.begin(), result.end(), result.begin(), ::toupper);
 
     return result;
   }
diff --git a/hex_functions.h b/hex_functions.h
index 9f7a1e7..1f22339 100644
--- a/hex_functions.h
+++ b/hex_functions.h
@@ -6,6 +6,8 @@
 #include <iostream>
 #include <algorithm>
 #include <string>
+#include <iomanip>
+#include <sstream>
 
 namespace omni
 {