diff --git a/hosts/mercury/configuration.nix b/hosts/mercury/configuration.nix
index 0e597e5..41fc9e8 100644
--- a/hosts/mercury/configuration.nix
+++ b/hosts/mercury/configuration.nix
@@ -21,6 +21,12 @@
   networking.interfaces.eth0.ipv4.addresses = [
     { address = "10.0.0.10"; prefixLength = 24; }     # the Pi's current IP
   ];
+  # Stable IPv6 (FRITZ!Box ULA prefix) so mercury is a fixed IPv6 DNS target.
+  # SLAAC still provides the GUA + default route. Announce THIS address as the
+  # DNSv6 server in the FRITZ!Box so IPv6 clients resolve .sol via pihole.
+  networking.interfaces.eth0.ipv6.addresses = [
+    { address = "fd18:df17:9078:0::10"; prefixLength = 64; }
+  ];
   # VERIFY with `ip route` on the Pi — assuming the router is .1.
   networking.defaultGateway = { address = "10.0.0.1"; interface = "eth0"; };
   # Resolvers for the Pi's OWN lookups (not the LAN service). Kept public so the