Index: head/sys/netinet/tcp_usrreq.c
===================================================================
--- head/sys/netinet/tcp_usrreq.c
+++ head/sys/netinet/tcp_usrreq.c
@@ -597,6 +597,10 @@
 			error = EINVAL;
 			goto out;
 		}
+		if ((inp->inp_vflag & INP_IPV4) == 0) {
+			error = EAFNOSUPPORT;
+			goto out;
+		}
 
 		in6_sin6_2_sin(&sin, sin6p);
 		inp->inp_vflag |= INP_IPV4;
@@ -614,6 +618,11 @@
 #endif
 		error = tp->t_fb->tfb_tcp_output(tp);
 		goto out;
+	} else {
+		if ((inp->inp_vflag & INP_IPV6) == 0) {
+			error = EAFNOSUPPORT;
+			goto out;
+		}
 	}
 #endif
 	inp->inp_vflag &= ~INP_IPV4;
Index: head/sys/netinet6/udp6_usrreq.c
===================================================================
--- head/sys/netinet6/udp6_usrreq.c
+++ head/sys/netinet6/udp6_usrreq.c
@@ -1119,6 +1119,10 @@
 			error = EINVAL;
 			goto out;
 		}
+		if ((inp->inp_vflag & INP_IPV4) == 0) {
+			error = EAFNOSUPPORT;
+			goto out;
+		}
 		if (inp->inp_faddr.s_addr != INADDR_ANY) {
 			error = EISCONN;
 			goto out;
@@ -1136,6 +1140,11 @@
 		if (error == 0)
 			soisconnected(so);
 		goto out;
+	} else {
+		if ((inp->inp_vflag & INP_IPV6) == 0) {
+			error = EAFNOSUPPORT;
+			goto out;
+		}
 	}
 #endif
 	if (!IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_faddr)) {