diff --git a/skeletons/asn_system.h b/skeletons/asn_system.h
index d391b7b..a992230 100644
--- a/skeletons/asn_system.h
+++ b/skeletons/asn_system.h
@@ -46,7 +46,7 @@
 typedef	unsigned short	uint16_t;
 typedef	unsigned int	uint32_t;
 #endif	/* ASSUMESTDTYPES */
-#define _WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 #include <float.h>
 #define isnan _isnan