diff --git a/include/chaiscript/language/chaiscript_engine.hpp b/include/chaiscript/language/chaiscript_engine.hpp
index a6a604a..9fbdd4c 100644
--- a/include/chaiscript/language/chaiscript_engine.hpp
+++ b/include/chaiscript/language/chaiscript_engine.hpp
@@ -36,7 +36,9 @@
 #else
 #ifdef CHAISCRIPT_WINDOWS
 #define VC_EXTRA_LEAN
+#if !defined(WIN32_LEAN_AND_MEAN)
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 #endif
 #endif