diff --git a/include/chaiscript/language/chaiscript_parser.hpp b/include/chaiscript/language/chaiscript_parser.hpp
index 32c24bf..1acb4f1 100644
--- a/include/chaiscript/language/chaiscript_parser.hpp
+++ b/include/chaiscript/language/chaiscript_parser.hpp
@@ -16,6 +16,7 @@
 #include <sstream>
 #include <string>
 #include <vector>
+#include <cctype>
 
 #include "../dispatchkit/boxed_value.hpp"
 #include "chaiscript_common.hpp"