diff --git a/src/nm-system.c b/src/nm-system.c
index 09e1da5865..bcff5092c2 100644
--- a/src/nm-system.c
+++ b/src/nm-system.c
@@ -1160,12 +1160,16 @@ replace_default_ip6_route (int ifindex, const struct in6_addr *gw, int mss)
 	char gw_str[INET6_ADDRSTRLEN + 1];
 
 	g_return_val_if_fail (ifindex > 0, FALSE);
-	g_return_val_if_fail (gw != NULL, FALSE);
 
 	if (nm_logging_level_enabled (LOGL_DEBUG)) {
-		memset (gw_str, 0, sizeof (gw_str));
-		if (inet_ntop (AF_INET6, gw, gw_str, sizeof (gw_str) - 1))
-			nm_log_dbg (LOGD_IP6, "Setting IPv6 default route via %s", gw_str);
+		if (gw) {
+			memset (gw_str, 0, sizeof (gw_str));
+			if (inet_ntop (AF_INET6, gw, gw_str, sizeof (gw_str) - 1))
+				nm_log_dbg (LOGD_IP6, "Setting IPv6 default route via %s", gw_str);
+		} else {
+			nm_log_dbg (LOGD_IP6, "Setting IPv6 default route via %s",
+			            nm_netlink_index_to_iface (ifindex));
+		}
 	}
 
 	/* We can't just use NLM_F_REPLACE here like in the IPv4 case, because