diff --git a/lib/Device.ml b/lib/Device.ml
index bc87443..571246b 100644
--- a/lib/Device.ml
+++ b/lib/Device.ml
@@ -8,7 +8,8 @@ module type DEVICE = sig
   val deo : Machine.machine -> int -> int -> unit
 end
 
-module Compose (D1 : DEVICE) (D2 : DEVICE) : DEVICE = struct
+module Compose (D1 : DEVICE) (D2 : DEVICE) :
+  DEVICE with type state = D1.state * D2.state = struct
   type state = D1.state * D2.state
 
   let state = (D1.state, D2.state)
diff --git a/shell.nix b/shell.nix
index d67efc2..6b2bc7e 100644
--- a/shell.nix
+++ b/shell.nix
@@ -4,6 +4,8 @@
 
 pkgs.mkShell {
   buildInputs = with pkgs; [
+    clang-tools
+    hyperfine
     xxd
     uxn
     ocamlPackages.ocaml
diff --git a/utils/Makefile b/utils/Makefile
index 7d48a98..6882f8e 100644
--- a/utils/Makefile
+++ b/utils/Makefile
@@ -3,7 +3,7 @@
 
 all: uxnmin drifloon.rom opctest.rom varvara.file.rom
 clean:
-	rm -f uxnmin drifloon.rom opctest.rom
+	rm -f uxnmin *.rom
 
 uxnmin: uxnmin.c
 drifloon.rom: uxnmin