diff --git a/ci.nix b/ci.nix
index 8fc5b46..af1552f 100644
--- a/ci.nix
+++ b/ci.nix
@@ -9,7 +9,7 @@
 # then your CI will be able to build and cache only those packages for
 # which this is possible.
 
-{ pkgs ? import <nixpkgs> { } }:
+{ pkgs ? import ./flake-compat.nix { src = ./.; } }:
 
 with builtins;
 
diff --git a/flake-compat.nix b/flake-compat.nix
new file mode 100644
index 0000000..68c4f5c
--- /dev/null
+++ b/flake-compat.nix
@@ -0,0 +1,12 @@
+{ src, system ? builtins.currentSystem or "unknown-system" }:
+
+let
+  lockFilePath = "${src}/flake.lock";
+  lockFile = builtins.fromJSON (builtins.readFile lockFilePath);
+  nixpkgs = lockFile.nodes.nixpkgs.locked;
+  tarball = fetchTarball {
+    url = "https://github.com/${nixpkgs.owner}/${nixpkgs.repo}/archive/${nixpkgs.rev}.zip";
+    sha256 = nixpkgs.narHash;
+  };
+in
+import tarball { inherit system; }