diff --git a/users/firewall.rst b/users/firewall.rst
index 2c7c07704..1516c53e2 100644
--- a/users/firewall.rst
+++ b/users/firewall.rst
@@ -30,7 +30,8 @@ incoming traffic:
 
 -  Port **22000/TCP** (or the actual listening port if you have changed
    the *Sync Protocol Listen Address* setting.)
--  Port **21025/UDP** (for discovery broadcasts)
+-  Port **21025/UDP** (for discovery broadcasts on IPv4)
+-  Port **21026/UDP** (for discovery multicasts on IPv6)
 
 Remote Web GUI
 --------------