diff --git a/src/forward.c b/src/forward.c
index 97180e5..3e2c769 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -724,7 +724,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
       /* Get extended RCODE. */
       rcode |= sizep[2] << 4;
       
-      if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, plen, pheader, query_source))
+      if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, n, pheader, query_source))
 	{
 	  my_syslog(LOG_WARNING, _("discarding DNS reply: subnet option mismatch"));
 	  return 0;