diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 2ed689a..0b1e7eb 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -123,9 +123,15 @@ ipv4_connected:
 				goto out;
 			}
 			sk->sk_bound_dev_if = usin->sin6_scope_id;
-			if (!sk->sk_bound_dev_if &&
-			    (addr_type & IPV6_ADDR_MULTICAST))
-				fl.oif = np->mcast_oif;
+		}
+
+		if ((addr_type & IPV6_ADDR_MULTICAST) && np->mcast_oif) {
+			if (sk->sk_bound_dev_if &&
+			    sk->sk_bound_dev_if != np->mcast_oif) {
+				err = -EINVAL;
+				goto out;
+			}
+			sk->sk_bound_dev_if = np->mcast_oif;
 		}
 
 		/* Connect to link-local address requires an interface */