diff --git a/skeletons/asn_system.h b/skeletons/asn_system.h
index 39a1f9e6..0a9b092c 100644
--- a/skeletons/asn_system.h
+++ b/skeletons/asn_system.h
@@ -37,6 +37,7 @@
 #ifndef __cplusplus
 #define inline __inline
 #endif
+#ifndef	ASSUMESTDTYPES	/* Standard types have been defined elsewhere */
 #define	ssize_t		SSIZE_T
 typedef	char		int8_t;
 typedef	short		int16_t;
@@ -44,6 +45,7 @@ typedef	int		int32_t;
 typedef	unsigned char	uint8_t;
 typedef	unsigned short	uint16_t;
 typedef	unsigned int	uint32_t;
+#endif	/* ASSUMESTDTYPES */
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 #include <float.h>