diff --git a/nix/infra/backend.nix b/nix/infra/backend.nix
index f51997a..992259a 100644
--- a/nix/infra/backend.nix
+++ b/nix/infra/backend.nix
@@ -15,7 +15,7 @@ in
     wantedBy = [ "multi-user.target" ];
     description = "Alisa Backend API Server";
     environment = {
-      DATABASE_URL = "postgres://${user}@localhost:${config.services.postgresql.settings.port}/${user}";
+      DATABASE_URL = ''postgres://${user}@localhost:${builtins.toString config.services.postgresql.settings.port}/${user}'';
       TOKEN_SECRET = "secret";
     };
     serviceConfig = {