diff --git a/controller/.gitignore b/controller/.gitignore
index da3d6f4..6097d0f 100644
--- a/controller/.gitignore
+++ b/controller/.gitignore
@@ -41,4 +41,8 @@ restic-password
 # App assets (synced from felhom.eu website at build time)
 assets/*.svg
 assets/*.png
-assets/*.webp
\ No newline at end of file
+assets/*.webp
+# build.sh's scratch directory. It is created beside the script, so a build run from a CLONE of
+# this repo (which is what the clean-tree gate pushes you to when the shared tree is busy) would
+# otherwise dirty the very tree the gate is checking. Generated output, never committed.
+workspace/