diff --git a/hive.nix b/hive.nix
index 175ea2a..2da30aa 100644
--- a/hive.nix
+++ b/hive.nix
@@ -26,6 +26,16 @@ in
     networking.useDHCP = false;
     services.openssh.enable = true;
 
+    # Enable system diffs.
+    system.activationScripts.system-diff = {
+      supportsDryActivation = true; # safe: only outputs to stdout
+      text = ''
+        if [ -e /run/current-system ]; then
+          PATH=$PATH:${pkgs.nix}/bin ${pkgs.nvd}/bin/nvd diff /run/current-system $systemConfig 
+        fi
+      '';
+    };
+
     # Mot de passe classique qu'on trouvera dans le "trousseau" legacy.
     users.users.root.initialHashedPassword = "$y$j9T$RoSZj8ezgR7cI8Le6xqwW/$0BI6G1Nqy/G0g0sNhQhyEedqoHsEyMFVjQgc3TPqE.4";
     system.stateVersion = "24.05";