diff --git a/npc/flake.nix b/npc/flake.nix
index 564efa0..15b910f 100644
--- a/npc/flake.nix
+++ b/npc/flake.nix
@@ -17,6 +17,7 @@
       in
       {
         devShells.default = with pkgs; mkShell {
+          CHISEL_FIRTOOL_PATH = "${nixpkgs-circt162.legacyPackages.${system}.circt}/bin";
           packages = [
             clang-tools
             # rnix-lsp