diff --git a/lagarto-ox.nix b/lagarto-ox.nix
index 14a0dec..fbe3da0 100644
--- a/lagarto-ox.nix
+++ b/lagarto-ox.nix
@@ -1,4 +1,4 @@
-{ config, lib, pkgs, modulesPath, ... }:
+{ config, lib, pkgs, modulesPath, self, ... }:
 
 {
   imports = [
@@ -175,8 +175,12 @@
     uboot-env = let
       init = "${config.system.build.toplevel}/init";
       initrd = "${config.system.build.initialRamdisk}/initrd";
+      rev = if self ? rev then self.rev
+        else throw ("Refusing to build from a dirty Git tree!");
     in prev.runCommand "uboot.txt" {} ''
       cat > $out <<EOF
+      # Git commit: ${rev}
+
       # Create pmem of 3 GiB [0x140000000, 0x200000000)
       fdt mknode / pmem@0x140000000
       fdt set /pmem@0x140000000 compatible "pmem-region"