diff --git a/flake.nix b/flake.nix
index 964683d..5f0dd02 100644
--- a/flake.nix
+++ b/flake.nix
@@ -27,10 +27,15 @@
         # Defaults applied to the bundled `nix` so it works on hosts
         # that don't already have nix set up (Arch/Debian/Fedora users
         # who install our .pkg.tar.zst / .deb / .rpm). Multi-user mode
-        # would expect a `nixbld` group and a running daemon
+        # would expect a `nixbld` group and a running daemon.
+        # `substituters` includes the cargoxx-pkgs binary cache so
+        # `cargoxx add <pkg>` substitutes prebuilt $out instead of
+        # rebuilding each registry package locally.
         cargoxxNixConfig = ''
           experimental-features = nix-command flakes
           build-users-group =
+          substituters = https://cache.cargoxx.amadey.xyz https://cache.nixos.org
+          trusted-public-keys = cache.cargoxx.amadey.xyz:HQNcKDh9lufWm0M32a06AEiLf1Hr0WoRY3Bp5NnWZxs= cache.nixos.org:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
         '';
 
         cargoxx-bin = pkgs.gcc15Stdenv.mkDerivation {