diff --git a/flake.nix b/flake.nix
index 7afea65..786b9ff 100644
--- a/flake.nix
+++ b/flake.nix
@@ -38,6 +38,7 @@
               agenix.nixosModules.default
               home-manager.nixosModules.default
               ({ config, ... }: {
+                nix.registry.nixpkgs.flake = nixpkgs; # pin `nix shell` nixpkgs
                 system.configurationRevision = nixpkgs.lib.mkIf (self ? rev) self.rev;
                 nixpkgs.overlays = getSystemOverlays config.nixpkgs.hostPlatform.system config.nixpkgs.config;
               })