diff --git a/conf.c b/conf.c
index 04e9956..f519a6a 100644
--- a/conf.c
+++ b/conf.c
@@ -263,7 +263,9 @@ static void conf_ports(const struct ctx *c, char optname, const char *optarg,
 			ifname++;
 		}
 
-		if (inet_pton(AF_INET, buf, addr))
+		if (ifname == buf + 1)		/* Interface without address */
+			addr = NULL;
+		else if (inet_pton(AF_INET, buf, addr))
 			af = AF_INET;
 		else if (inet_pton(AF_INET6, buf, addr))
 			af = AF_INET6;
diff --git a/passt.1 b/passt.1
index 4c90634..cb7ae4e 100644
--- a/passt.1
+++ b/passt.1
@@ -385,6 +385,9 @@ Forward local port 22, bound to 192.0.2.1, to port 22 on the guest
 -t 192.0.2.1%eth0/22
 Forward local port 22, bound to 192.0.2.1 and interface eth0, to port 22
 .TP
+-t %eth0/22
+Forward local port 22, bound to any address on interface eth0, to port 22
+.TP
 -t 2000-5000,~3000-3010
 Forward local ports between 2000 and 5000, except for those between 3000 and
 3010
@@ -467,6 +470,9 @@ Forward local port 22, bound to 192.0.2.1, to port 22 in the target namespace
 -t 192.0.2.1%eth0/22
 Forward local port 22, bound to 192.0.2.1 and interface eth0, to port 22
 .TP
+-t %eth0/22
+Forward local port 22, bound to any address on interface eth0, to port 22
+.TP
 -t 2000-5000,~3000-3010
 Forward local ports between 2000 and 5000, except for those between 3000 and
 3010