diff --git a/sys/netinet/in.h b/sys/netinet/in.h
--- a/sys/netinet/in.h
+++ b/sys/netinet/in.h
@@ -418,8 +418,32 @@
 #define	IN_RFC3021_MASK		((in_addr_t)0xfffffffe)
 
 #ifdef _KERNEL
+#include "opt_inet.h"
+#include "opt_inet6.h"
+
 #include <net/vnet.h>
 
+/*
+ * Define an enum with only the relevant address families (i.e. no IPv4 for a
+ * NOINET kernel) so that we can forgo a default case for 'switch (af)'.
+ * We deliberately set the values to be the same as sa_family_t, which is what
+ * we traditionally used in such cases, so that it's less risky to mix types.
+ */
+typedef enum {
+#ifndef AF_INET
+#define AF_INET		2
+#endif
+#ifndef AF_INET6
+#define AF_INET6	28
+#endif
+#ifdef INET
+	IP_AF_4 = AF_INET,
+#endif
+#ifdef INET6
+	IP_AF_6 = AF_INET6,
+#endif
+} ip_af_t;
+
 VNET_DECLARE(bool, ip_allow_net0);
 VNET_DECLARE(bool, ip_allow_net240);
 /* Address space reserved for loopback */
diff --git a/sys/netinet/libalias/alias_sctp.h b/sys/netinet/libalias/alias_sctp.h
--- a/sys/netinet/libalias/alias_sctp.h
+++ b/sys/netinet/libalias/alias_sctp.h
@@ -166,9 +166,8 @@
 	uint16_t msg;			/**< one of the key messages defined above */
 #ifdef INET6
 	//  struct ip6_hdr *ip_hdr;	/**< pointer to ip packet header */ /*no inet6 support yet*/
-#else
-	struct ip *ip_hdr;		/**< pointer to ip packet header */
 #endif //#ifdef INET6
+	struct ip *ip_hdr;		/**< pointer to ip packet header */
 	struct sctphdr *sctp_hdr;	/**< pointer to sctp common header */
 	union sctpChunkOfInt sctpchnk; /**< union of pointers to the chunk of interest */
 	int chunk_length;		/**< length of chunk of interest */