diff --git a/rebuild.sh b/rebuild.sh
index f2d37bd..1197209 100755
--- a/rebuild.sh
+++ b/rebuild.sh
@@ -4,6 +4,14 @@ pushd ~/.nix
 # nvim flake.nix
 # alejandra . &>/dev/null
 git diff -U0 *.nix
+
+# add generation comment to flake.nix
+if grep -q '^# generation:' flake.nix; then
+    sed -i "1s/^# generation:.*/# generation: $gen/" flake.nix
+else
+    sed -i "1i# generation: $gen" flake.nix
+fi
+
 echo "nixos rebuilding..."
 sudo nixos-rebuild switch --flake ~/.nix#snowbelle &>.nixos-switch-log || (
  cat nixos-switch.log | grep --color error && false)