diff --git a/pkgs/http-fstree/http-fstree.fnl b/pkgs/http-fstree/http-fstree.fnl
index 6e83a19..4f578c1 100644
--- a/pkgs/http-fstree/http-fstree.fnl
+++ b/pkgs/http-fstree/http-fstree.fnl
@@ -9,8 +9,13 @@
     (assert nil (.. "error " code ": " str))
 
     (body { : last-modified })
-    (let [service (svc.open dest)]
+    (let [service (svc.open dest)
+          lock (.. dest "/.lock")
+          state (.. dest "/state")]
+      (with-open [fout (io.open lock :w)] (fout:write ""))
       (service:output "." (json.decode body))
+      (with-open [fout (io.open state :w)] (fout:write "ok"))
+      (os.remove lock)
       (utime dest last-modified))))
 
 (fn run [] (download (. arg 1) (. arg 2)))