diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9b04296..8f1d7c1 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -38,7 +38,7 @@ jobs:
 
       - run:
           name: Nix build
-          command: nix-build --sandbox --no-link --cores 0 ./test.nix
+          command: ./script/test
 
 workflows:
   version: 2
diff --git a/nix/default.nix b/nix/default.nix
new file mode 100644
index 0000000..2678dc1
--- /dev/null
+++ b/nix/default.nix
@@ -0,0 +1,4 @@
+{ system ? builtins.currentSystem }:
+let
+  sources = import ./sources.nix;
+in import sources.nixpkgs { inherit system; }
diff --git a/script/test b/script/test
new file mode 100755
index 0000000..3cf5495
--- /dev/null
+++ b/script/test
@@ -0,0 +1,18 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash
+#!nix-shell -I nixpkgs=./nix
+#!nix-shell -p nix
+#!nix-shell --pure
+#!nix-shell --keep SSL_CERT_FILE
+#!nix-shell --keep NIX_SSL_CERT_FILE
+
+set -euo pipefail
+
+export NIX_PATH="nixpkgs=./nix"
+
+echo "Building"
+
+# Build and create a root
+nix-build ./test.nix --sandbox --no-link --max-jobs 10
+
+echo "all good"
diff --git a/test.nix b/test.nix
index ef0c96d..683f339 100644
--- a/test.nix
+++ b/test.nix
@@ -1,7 +1,7 @@
 { system ? builtins.currentSystem }:
 let
   sources = import ./nix/sources.nix;
-  pkgs = import sources.nixpkgs { inherit system; };
+  pkgs = import ./nix { inherit system; };
   naersk = pkgs.callPackage ./default.nix
     { inherit (pkgs.rustPackages) cargo rustc; };
   builtinz = builtins // pkgs.callPackage ./builtins {};