diff --git a/services/router.nix b/services/router.nix
index 9f4a9bb..79081a6 100644
--- a/services/router.nix
+++ b/services/router.nix
@@ -69,6 +69,7 @@ in
       "net.ipv4.ip_forward" = 1;
       "net.ipv4.conf.all.rp_filter" = 1;
       "net.ipv6.conf.all.forwarding" = 0;  # no IPv6 upstream yet
+      "net.ipv6.conf.all.disable_ipv6" = 1;
     };
 
     # --- Interface configuration ---