diff --git a/docs/internal-fs-layout.md b/docs/internal-fs-layout.md
index 401ebda1..f63978f3 100644
--- a/docs/internal-fs-layout.md
+++ b/docs/internal-fs-layout.md
@@ -42,8 +42,12 @@ For example, if you want to change the manifest branch, you can simply run
     change the git URL/branch that this tracks, re-run `repo init` with the new
     settings.
 
-*   `.repo_fetchtimes.json`: Used by `repo sync` to record stats when syncing
-    the various projects.
+*   `.repo_fetchtimes.json`: Used by `repo sync` to record fetch times when
+    syncing the various projects.
+
+*   `.repo_localsyncstate.json`: Used by `repo sync` to detect and warn on
+    on partial tree syncs.  Partial syncs are allowed by `repo` itself, but are
+    unsupported by many projects where `repo` is used.
 
 ### Manifests