diff --git a/flake.nix b/flake.nix
index 79fa6e9..d77dc22 100644
--- a/flake.nix
+++ b/flake.nix
@@ -28,17 +28,21 @@
         query = {
           ocaml-base-compiler = "*";
         };
+        overlay = final: prev: {
+          "${package}" = prev.${package}.overrideAttrs (o: {
+            passthru = o.passthru // {
+              shellPath = "/bin/msh";
+            };
+          });
+        };
         scope =
           # recursive finds vendored dependancies in duniverse
-          opam-nix-lib.buildOpamProject' { recursive = true; } ./. (query // devPackagesQuery);
+          (opam-nix-lib.buildOpamProject' { recursive = true; } ./. (query // devPackagesQuery)).overrideScope
+            overlay;
       in {
         packages.default = scope.${package};
         defaultPackage = scope.${package};
 
-        passthru = {
-          shellPath = "/bin/msh";
-        };
-
         devShells.default = let
           devPackages = builtins.attrValues
             (pkgs.lib.getAttrs (builtins.attrNames devPackagesQuery) scope);