Freezes while cloning nixpkgs (presumably)

[fakedrake]

Here is my default.nix

{ nixpkgs ? import <nixpkgs> {}
, racket2nix ? nixpkgs.fetchFromGitHub {
  owner = "fractalide"; repo = "racket2nix";
  rev = "59c614406d4796f40620f6490b0b05ecb51ed976";
  sha256 = "0z5y1jm60vkwvi66q39p88ygkgyal81486h577gikmpqjxkg9d6i"; }
}:

let
  r2n = import racket2nix {};
in r2n.buildRacketPackage "spvector"

And when I try to build it "reading bytes" and "waiting for children" approximately every second.

$ nix-build -vvvvv
...
building '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv'...
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 177 bytes
exporting https://github.com/NixOS/nixpkgs-channels.git (rev 1bf18e4c852c52e13842e71f70dec1752bb4297b) into /nix/store/h6dcxhwm59l28yq3c80biqp8yi0hqmgr-nixpkgs-channels-1bf18e4
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 111 bytes
Initialized empty Git repository in /nix/store/h6dcxhwm59l28yq3c80biqp8yi0hqmgr-nixpkgs-channels-1bf18e4/.git/
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 1024 bytes
remote: Enumerating objects: 2073191, done.
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 1024 bytes
remote: Counting objects: 100% (28/28), done.
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 106 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 322 bytes
remote: Compressing objects: 100% (26/26), done.
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 36 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 63 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 63 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 63 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children
building of '/nix/store/g9hsc65vp037rayicggf6n3h861q942h-nixpkgs-channels-1bf18e4.drv': read 64 bytes
waiting for children