diff --git a/dev/treefmt.nix b/dev/treefmt.nix
index 2f80e31..2181222 100644
--- a/dev/treefmt.nix
+++ b/dev/treefmt.nix
@@ -67,7 +67,7 @@
         "-eucx"
         ''
           ${pkgs.lib.getExe pkgs.ruff} --fix "$@"
-          ${pkgs.lib.getExe pkgs.python3.pkgs.black} "$@"
+          ${pkgs.lib.getExe pkgs.ruff} format "$@"
         ''
         "--" # this argument is ignored by bash
       ];