diff --git a/README.md b/README.md
index 5d6c327..332bf77 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,12 @@ nix run github:nix-community/nixos-anywhere -- --flake .#<somehost> root@<someho
 nix-shell -p nixUnstable --run 'nixos-install --flake https://gitlab.jalr.de/jalr/nixos-configuration#somehost --no-channel-copy'
 ```
 
+### Build a configuration
+
+```
+nix build .#nixosConfigurations.iron.config.system.build.toplevel
+```
+
 ### setting up sops
 Get the host key and convert it.
 ```bash