diff --git a/default.nix b/default.nix
index 9d9784d5f4b9c2b56d1a0f31fb39cffd6db8f8ad..6441675a243e22e6154267c656652c8d8575940e 100644
--- a/default.nix
+++ b/default.nix
@@ -6,9 +6,9 @@
 
   # Run some system integration tests in VMs covering some of the software
   # we're integrating (ie, application functionality).
-  system-tests = import ./nixos/system-tests.nix;
+  system-tests = pkgs.callPackage ./nixos/system-tests.nix { };
 
   # Run some unit tests of the Nix that ties all of these things together (ie,
   # PrivateStorageio-internal library functionality).
-  unit-tests = import ./nixos/unit-tests.nix;
+  unit-tests = pkgs.callPackage ./nixos/unit-tests.nix { };
 }
diff --git a/nixos/system-tests.nix b/nixos/system-tests.nix
index 7b6d382ada53c1121a1bc3d0edbf82964d644ad2..218132fe2cd3857f4c201085b4df56a411c794d4 100644
--- a/nixos/system-tests.nix
+++ b/nixos/system-tests.nix
@@ -1,7 +1,6 @@
 # The overall system test suite for PrivateStorageio NixOS configuration.
-let
-  pkgs = import ../nixpkgs-2105.nix { };
-in {
+{ pkgs }:
+{
   private-storage = pkgs.nixosTest ./tests/private-storage.nix;
   spending = pkgs.nixosTest ./tests/spending.nix;
   tahoe = pkgs.nixosTest ./tests/tahoe.nix;
diff --git a/nixos/unit-tests.nix b/nixos/unit-tests.nix
index 75016a17d128fabe11f4ecaad65dba3471ed863d..b9f72bf95901af2668d68d1a09814c2bc2a9cd93 100644
--- a/nixos/unit-tests.nix
+++ b/nixos/unit-tests.nix
@@ -1,7 +1,6 @@
 # The overall unit test suite for PrivateStorageio NixOS configuration.
+{ pkgs }:
 let
-  pkgs = import <nixpkgs> { };
-
   # Total the numbers in a list.
   sum = builtins.foldl' (a: b: a + b) 0;