diff --git a/.circleci/config.yml b/.circleci/config.yml
index 276e0c520002eb6ef3e3bb14b9c383659baba27b..2fda09c7eb1ef31545cce667df22a50ea5602a19 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -18,6 +18,10 @@ jobs:
   test:
     docker:
       - image: "nixos/nix:2.2.1"
+
+    environment:
+      NIX_PATH: "nixpkgs=https://github.com/NixOS/nixpkgs/archive/3c83ad6ac13b67101cc3e2e07781963a010c1624.tar.gz"
+
     steps:
       - run:
           name: "Install Git"
diff --git a/shell.nix b/shell.nix
index 5963efcdb61e1097b0d0fe0c748ecf2f1ce898db..b474e0029a87c9da6fcdec474f80089c1aa05a2c 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,12 +1,6 @@
-let
-  pinnedPkgs = import (builtins.fetchTarball {
-    url = "https://github.com/NixOS/nixpkgs/archive/3c83ad6ac13b67101cc3e2e07781963a010c1624.tar.gz";
-    sha256 = "0cdq342wrkvkyccygpp1gvwp7hhqg68hljjwld4vjixm901ayy14";
-  }) {};
-in
-{ ... }:
-pinnedPkgs.mkShell {
+{ pkgs ? import <nixpkgs> { } }:
+pkgs.mkShell {
   buildInputs = [
-    pinnedPkgs.stack
+    pkgs.stack
   ];
 }