diff --git a/share/man/man4/siftr.4 b/share/man/man4/siftr.4
index 28e38e56d4c0..75fb6c643ddd 100644
--- a/share/man/man4/siftr.4
+++ b/share/man/man4/siftr.4
@@ -30,7 +30,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 18, 2015
+.Dd October 7, 2019
 .Dt SIFTR 4
 .Os
 .Sh NAME
@@ -131,6 +131,14 @@ The hashes are useful to correlate which TCP packet triggered the generation of
 a particular log message, but calculating them adds additional computational
 overhead into the fast path.
 .El
+.Bl -tag -offset indent -width Va
+.It Va net.inet.siftr.port_filter
+controls on which source or destination port siftr should capture
+.Nm .
+By default, the value is set to 0, which means all ports are eligible for logging.
+Set to any other value, only packets where either the source or destination
+port is equal to this number are logged.
+.El
 .Ss Log Format
 A typical
 .Nm
diff --git a/sys/netinet/siftr.c b/sys/netinet/siftr.c
index c251fb44c8bc..e93bcf79b223 100644
--- a/sys/netinet/siftr.c
+++ b/sys/netinet/siftr.c
@@ -918,7 +918,7 @@ siftr_chkpkt(struct mbuf **m, struct ifnet *ifp, int flags,
 	 * Only pkts selected by the tcp port filter
 	 * can be inserted into the pkt_queue
 	 */
-	if ((siftr_port_filter != 0) && 
+	if ((siftr_port_filter != 0) &&
 	    (siftr_port_filter != ntohs(inp->inp_lport)) &&
 	    (siftr_port_filter != ntohs(inp->inp_fport))) {
 		goto inp_unlock;