diff --git a/nix/host-modules/hive-network.nix b/nix/host-modules/hive-network.nix
index a50b12d2..02abad58 100644
--- a/nix/host-modules/hive-network.nix
+++ b/nix/host-modules/hive-network.nix
@@ -184,21 +184,28 @@ in
             backstop.
           '';
         }
+      ];
+    })
+
+    # Un-gated: the swarm's options are identical on every host, so a host
+    # running no hive and no swarm service needs the value too. The
+    # `.invalid` fallbacks described above keep this message reachable.
+    {
+      assertions = [
         {
           assertion = config.services.hyperhive.swarm.domain != null;
           message = ''
-            hyperhive requires services.hyperhive.swarm.domain to be
-            set — the DNS domain of the swarm this hive belongs to,
-            of which this hive occupies one sub-domain. There is no
-            fallback: a guessed value would be a wrong hostname that
-            evaluates cleanly and deploys. Set it
-            (`services.hyperhive.swarm.domain = "example.com";`) —
-            with `hiveName` it also derives
-            `services.hyperhive.domain` for you.
+            hyperhive requires services.hyperhive.swarm.domain to be set
+            on every host, to the same value on every host of the swarm —
+            the DNS domain of the swarm, of which each hive occupies one
+            sub-domain. There is no fallback: a guessed value would be a
+            wrong hostname that evaluates cleanly and deploys. Set it
+            (`services.hyperhive.swarm.domain = "example.com";`) — with
+            `hiveName` it also derives `services.hyperhive.domain` for you.
           '';
         }
       ];
-    })
+    }
 
     # The bridge itself, up only where something hangs off it. Private
     # netns is still the only container mode.
diff --git a/nix/host-modules/hyperhive.nix b/nix/host-modules/hyperhive.nix
index 83f7c200..2eed26b5 100644
--- a/nix/host-modules/hyperhive.nix
+++ b/nix/host-modules/hyperhive.nix
@@ -117,9 +117,9 @@ in
       `services.hyperhive.hiveName`, list the hives by name, and no
       hive in the swarm states an address at all.
 
-      **Required** when
-      `services.hyperhive.deploy.hive-controller.enable`, and deliberately
-      not defaulted: there is no fallback worth having. A guessed
+      **Required** on every host that imports this module, with the
+      same value on every host of the swarm, and deliberately not
+      defaulted: there is no fallback worth having. A guessed
       swarm domain is a wrong hostname that evaluates cleanly and
       deploys, which is worse than an eval failure telling an
       operator to write down the one address their swarm answers to.