diff --git a/modules/default.nix b/modules/default.nix
index cd44080..4d030f8 100644
--- a/modules/default.nix
+++ b/modules/default.nix
@@ -127,7 +127,10 @@ in
   config = lib.mkIf cfg.enable {
 
     environment.systemPackages = [ pkgs.tvix ];
-    users.users.tvix-castore = { };
+    users.users.tvix-castore = {
+      isSystemUser = true;
+      group = "tvix-castore";
+    };
     users.groups.tvix-castore = { };
 
     systemd.tmpfiles.rules = [ "d ${cfg.castoreDir} 770 root tvix-castore -" ];