diff --git a/system/nixos/mastodon.nix b/system/nixos/mastodon.nix
index 7138f05..b4738f3 100644
--- a/system/nixos/mastodon.nix
+++ b/system/nixos/mastodon.nix
@@ -100,7 +100,7 @@ in
     };
   };
 
-  users.groups.mastodon.members = config.services.nginx.user;
+  users.groups.mastodon.members = [ config.services.nginx.user ];
 
   networking.firewall.allowedTCPPorts = [ 80 ];
 }