diff --git a/newlib/libc/sys/rtems/include/netinet/in.h b/newlib/libc/sys/rtems/include/netinet/in.h
index 059f50d9b..4c692b6df 100644
--- a/newlib/libc/sys/rtems/include/netinet/in.h
+++ b/newlib/libc/sys/rtems/include/netinet/in.h
@@ -342,10 +342,15 @@ __END_DECLS
 #define	IPPORT_MAX		65535
 
 /*
- * Definitions of bits in internet address integers.
- * On subnets, the decomposition of addresses to host and net parts
- * is done according to subnet mask, not the masks here.
+ * Historical definitions of bits in internet address integers
+ * (pre-CIDR).  Class A/B/C are long obsolete, and now deprecated.
+ * Hide these definitions from the kernel unless IN_HISTORICAL_NETS
+ * is defined.  Provide the historical definitions to user level for now.
  */
+#ifndef _KERNEL
+#define IN_HISTORICAL_NETS
+#endif
+#ifdef IN_HISTORICAL_NETS
 #define	IN_CLASSA(i)		(((in_addr_t)(i) & 0x80000000) == 0)
 #define	IN_CLASSA_NET		0xff000000
 #define	IN_CLASSA_NSHIFT	24
@@ -362,12 +367,17 @@ __END_DECLS
 #define	IN_CLASSC_NET		0xffffff00
 #define	IN_CLASSC_NSHIFT	8
 #define	IN_CLASSC_HOST		0x000000ff
+#endif /* IN_HISTORICAL_NETS */
 
-#define	IN_CLASSD(i)		(((in_addr_t)(i) & 0xf0000000) == 0xe0000000)
+#define	IN_NETMASK_DEFAULT	0xffffff00	/* mask when forced to guess */
+
+#define	IN_MULTICAST(i)		(((in_addr_t)(i) & 0xf0000000) == 0xe0000000)
+#ifdef IN_HISTORICAL_NETS
+#define	IN_CLASSD(i)		IN_MULTICAST(i)
 #define	IN_CLASSD_NET		0xf0000000	/* These ones aren't really */
 #define	IN_CLASSD_NSHIFT	28		/* net and host fields, but */
 #define	IN_CLASSD_HOST		0x0fffffff	/* routing needn't know.    */
-#define	IN_MULTICAST(i)		IN_CLASSD(i)
+#endif /* IN_HISTORICAL_NETS */
 
 #define	IN_EXPERIMENTAL(i)	(((in_addr_t)(i) & 0xf0000000) == 0xf0000000)
 #define	IN_BADCLASS(i)		(((in_addr_t)(i) & 0xf0000000) == 0xf0000000)
@@ -398,7 +408,9 @@ __END_DECLS
 #define	INADDR_ALLMDNS_GROUP	((in_addr_t)0xe00000fb)	/* 224.0.0.251 */
 #define	INADDR_MAX_LOCAL_GROUP	((in_addr_t)0xe00000ff)	/* 224.0.0.255 */
 
+#ifdef IN_HISTORICAL_NETS
 #define	IN_LOOPBACKNET		127			/* official! */
+#endif /* IN_HISTORICAL_NETS */
 
 #define	IN_RFC3021_MASK		((in_addr_t)0xfffffffe)