diff --git a/nix/default.nix b/nix/default.nix
index 3df7c26e4335d891a42e3baad09780193c42287f..1f9c55741073aeabb4bff3bcee3e25d420258d7a 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -1,5 +1,5 @@
 # paramaterised derivation with dependencies injected (callPackage style)
-{ pkgs, stdenv, src ? ../., opam2nix, ocaml ? "ocaml-ng.ocamlPackages_4_08.ocaml", plugins ? { } }:
+{ pkgs, stdenv, src ? ../., opam2nix, ocaml ? pkgs.ocaml-ng.ocamlPackages_4_08.ocaml, plugins ? { } }:
 
 let mydir = builtins.getEnv("PWD");
     mk-opam-selection = name: {