diff --git a/nix/nixos-module/container/upstream/pppoe.nix b/nix/nixos-module/container/upstream/pppoe.nix
index cfa5c9f..424a99d 100644
--- a/nix/nixos-module/container/upstream/pppoe.nix
+++ b/nix/nixos-module/container/upstream/pppoe.nix
@@ -81,11 +81,13 @@ in lib.mkIf (pppoeInterfaces != {}) {
       };
     }) {} (builtins.attrNames pppoeInterfaces);
 
-  # TODO: needed?
   networking.nat.extraCommands = ''
     iptables -A FORWARD \
       -p tcp --tcp-flags SYN,RST SYN \
       -j TCPMSS --clamp-mss-to-pmtu
+    ip6tables -A FORWARD \
+      -p tcp --tcp-flags SYN,RST SYN \
+      -j TCPMSS --clamp-mss-to-pmtu
   '';
 
 }