Nix: Skipping unit tests when installing a Haskell package

I'm using Nix to install packages under my home (so no binary packages) on a shared host with limited resources. I'm trying to install git-annex. When building one of its dependencies, haskell-lens, the unit tests consume so much memory that they get killed and the installation fails. Is there a way to skip the unit tests to get the package installed? I looked at the Cabal builder and haskell-packages.nix and it seems to me that you could disable the tests by setting enableCheckPhase to false. I tried the following in ~/.nixpkgs/config.nix, but the tests are still run: { packageOverrides = pkgs: with pkgs; { # ...other customizations... haskellPackages = haskellPackages.override { extension = self : super : { self.lens = self.disableTest self.lens; }; }; }; }