diff --git a/nixos/roles/rabbitmq.nix b/nixos/roles/rabbitmq.nix
index b8648e26c..074beed24 100644
--- a/nixos/roles/rabbitmq.nix
+++ b/nixos/roles/rabbitmq.nix
@@ -40,6 +40,7 @@ in
     enabledRolesCount = length (lib.attrNames enabledRoles);
     enabled = enabledRolesCount > 0;
     roleVersion = head (lib.attrNames enabledRoles);
+    isSingleNode = length (fclib.findServices "rabbitmq-node") == 1;
   in
   lib.mkMerge [
 
@@ -51,6 +52,15 @@ in
       flyingcircus.services.rabbitmq.enable = true;
     })
 
+    # For single-node setups of current RabbitMQ versions, set feature flags
+    # automatically after platform upgrades. This is the easy and common case.
+    # Cluster setups require manual intervention for enabling feature flags.
+    # Note that we simply check the number of rabbitmq instances in the RG to be safe,
+    # we don't know here if they actually form a cluster.
+    (lib.mkIf (config.flyingcircus.roles.rabbitmq.enable && isSingleNode) {
+      systemd.services.rabbitmq.postStart = "rabbitmqctl enable_feature_flag all";
+    })
+
     (lib.mkIf enabled {
       assertions =
         [
@@ -83,11 +93,5 @@ in
         }
       ];
     }
-
-    {
-      systemd.services.rabbitmq.postStart = lib.optionalString ((length (fclib.findServices "rabbitmq-node")) == 1) ''
-          rabbitmqctl enable_feature_flag all
-        '';
-    }
   ];
 }