Index: netinet/tcp_usrreq.c
===================================================================
--- netinet/tcp_usrreq.c
+++ netinet/tcp_usrreq.c
@@ -595,6 +595,11 @@
 			error = EINVAL;
 			goto out;
 		}
+		if (inp->inp_lport != 0 &&
+		   !IN6_IS_ADDR_V4COMPAT(&inp->in6p_laddr)) {
+			error = EAFNOSUPPORT;
+			goto out;
+		}
 
 		in6_sin6_2_sin(&sin, sin6p);
 		inp->inp_vflag |= INP_IPV4;
Index: netinet6/in6_src.c
===================================================================
--- netinet6/in6_src.c
+++ netinet6/in6_src.c
@@ -280,6 +280,8 @@
 		    (error = prison_local_ip6(cred, &inp->in6p_laddr,
 		    ((inp->inp_flags & IN6P_IPV6_V6ONLY) != 0))) != 0)
 			return (error);
+		if (IN6_IS_ADDR_V4COMPAT(&inp->in6p_laddr))
+			return (EAFNOSUPPORT);
 		bcopy(&inp->in6p_laddr, srcp, sizeof(*srcp));
 		return (0);
 	}