diff --git a/pkgs/os-specific/linux/systemd/default.nix b/pkgs/os-specific/linux/systemd/default.nix
index 596156c4f792..7e3c6d1fe51f 100644
--- a/pkgs/os-specific/linux/systemd/default.nix
+++ b/pkgs/os-specific/linux/systemd/default.nix
@@ -1,3 +1,5 @@
+# NOTE: Make sure to (re-)format this file on changes with `nixpkgs-fmt`!
+
 { stdenv
 , lib
 , fetchFromGitHub