diff --git a/miniupnpd/miniupnpd.c b/miniupnpd/miniupnpd.c
index 40c727d..1c6367c 100644
--- a/miniupnpd/miniupnpd.c
+++ b/miniupnpd/miniupnpd.c
@@ -1,4 +1,4 @@
-/* $Id: miniupnpd.c,v 1.242 2020/04/09 18:38:14 nanard Exp $ */
+/* $Id: miniupnpd.c,v 1.243 2020/04/12 17:43:13 nanard Exp $ */
 /* vim: tabstop=4 shiftwidth=4 noexpandtab
  * MiniUPnP project
  * http://miniupnp.free.fr/ or http://miniupnp.tuxfamily.org/
@@ -2115,6 +2115,7 @@ main(int argc, char * * argv)
 		} else if (addr_is_reserved(&addr)) {
 			syslog(LOG_INFO, "Reserved / private IP address %s on ext interface %s: Port forwarding is impossible", if_addr, ext_if_name);
 			syslog(LOG_INFO, "You are probably behind NAT, enable option ext_perform_stun=yes to detect public IP address");
+			syslog(LOG_INFO, "Or use ext_ip= / -o option to declare public IP address");
 			disable_port_forwarding = 1;
 		}
 	}
diff --git a/miniupnpd/miniupnpd.conf b/miniupnpd/miniupnpd.conf
index 1d8cbd5..5337c65 100644
--- a/miniupnpd/miniupnpd.conf
+++ b/miniupnpd/miniupnpd.conf
@@ -5,7 +5,9 @@
 # set ext_ifname6
 #ext_ifname6=eth2
 # If the WAN interface has several IP addresses, you
-# can specify the one to use below
+# can specify the one to use below.
+# Setting ext_ip is also useful in double NAT setup, you can declare here
+# the public IP address.
 #ext_ip=
 # WAN interface must have public IP address. Otherwise it is behind NAT
 # and port forwarding is impossible. In some cases WAN interface can be