diff --git a/desktop_version/src/UtilityClass.cpp b/desktop_version/src/UtilityClass.cpp
index f3e27eca..06859db2 100644
--- a/desktop_version/src/UtilityClass.cpp
+++ b/desktop_version/src/UtilityClass.cpp
@@ -2,6 +2,7 @@
 
 #include "SDL.h"
 
+#include <cctype>
 #include <sstream>
 
 /* Used by UtilityClass::GCString to generate a button list */