diff --git a/flake.nix b/flake.nix
index 10b84fa..6ff8480 100644
--- a/flake.nix
+++ b/flake.nix
@@ -28,7 +28,9 @@
               nixVersion = "unstable";
             };
           };
-          devShells.default = pkgs.callPackage ./shell.nix { };
+          devShells.default = pkgs.callPackage ./shell.nix {
+            packages = [ config.treefmt.build.wrapper ];
+          };
           apps.test-runner = {
             type = "app";
             program = "${config.packages.test-runner}";
diff --git a/shell.nix b/shell.nix
index 87e4645..d32920a 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,8 +1,8 @@
-{ pkgs ? import <nixpkgs> { } }:
+{ pkgs ? import <nixpkgs> { }, packages ? [ ] }:
 
 with pkgs;
 mkShell {
-  nativeBuildInputs = [
+  packages = packages ++ [
     python3.pkgs.pytest
     python3.pkgs.mypy
     ruff