diff --git a/ext/socket/mkconstants.rb b/ext/socket/mkconstants.rb
index f1f450d..73bc9fe 100644
--- a/ext/socket/mkconstants.rb
+++ b/ext/socket/mkconstants.rb
@@ -622,6 +622,7 @@ TCP_NOPUSH	nil	Don't push the last block of write
 TCP_QUICKACK	nil	Enable quickack mode
 TCP_SYNCNT	nil	Number of SYN retransmits before a connection is dropped
 TCP_WINDOW_CLAMP	nil	Clamp the size of the advertised window
+TCP_FASTOPEN nil Reduce step of the handshake process
 
 UDP_CORK	nil	Don't send partial frames