diff --git a/man7/tcp.7 b/man7/tcp.7
index 2c979c3ae..ed10506c7 100644
--- a/man7/tcp.7
+++ b/man7/tcp.7
@@ -232,6 +232,16 @@ are reserved for the application buffer.
 A value of 0
 implies that no amount is reserved.
 .\"
+.\" The following is from 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
+.TP
+.IR tcp_base_mss "(Integer; default: 512; since Linux 2.6.17)
+The initial value of
+.I search_low
+to be used by the packetization layer
+Path MTU discovery (MTU probing).
+If MTU probing is enabled,
+this is the initial MSS used by the connection.
+.\"
 .\" The following is from 2.6.12: Documentation/networking/ip-sysctl.txt
 .TP
 .IR tcp_bic " (Boolean; default: disabled)"