NobbZ: infinisil thanks, this is now building:
```nix
    psi-plus = unstable-nixpkgs.pkgs.psi-plus.overrideAttrs (srcAttrs: srcAttrs // rec {
      version = "1.4.1463";

      src = pkgs.fetchFromGitHub {
        owner = "psi-plus";
        repo = "psi-plus-snapshots";
        rev = version;
        sha256 = "0x1ck2rdk51n99jzv291qg745y8f42prpm11xgn9m3li0hn47di7";
      };
    });
```