diff --git a/modules/services/nix-optimise/default.nix b/modules/services/nix-optimise/default.nix
index 4eefc48..addf046 100644
--- a/modules/services/nix-optimise/default.nix
+++ b/modules/services/nix-optimise/default.nix
@@ -52,15 +52,20 @@ in
 
   ###### implementation
 
-  config = mkIf cfg.automatic {
+  config = {
+    assertions = [
+      {
+        assertion = cfg.automatic -> config.nix.enable;
+        message = ''nix.optimise.automatic requires nix.enable'';
+      }
+    ];
 
-    launchd.daemons.nix-optimise = {
+    launchd.daemons.nix-optimise = mkIf cfg.automatic {
       command = "${lib.getExe' config.nix.package "nix-store"} --optimise";
       serviceConfig = {
         RunAtLoad = false;
         StartCalendarInterval = cfg.interval;
       };
     };
-
   };
 }