diff --git a/web.py b/web.py
index 50932ff..2963a0a 100644
--- a/web.py
+++ b/web.py
@@ -363,7 +363,8 @@ class _Handler(BaseHTTPRequestHandler):
         try:
             cached = json.loads(cache_path.read_text('utf-8'))
             if cached.get('threshold') == threshold and cached.get('min_gap') == min_gap:
-                self._send(200, json.dumps(cached['result']).encode('utf-8'), 'application/json')
+                payload = dict(cached['result']); payload['cached'] = True
+                self._send(200, json.dumps(payload).encode('utf-8'), 'application/json')
                 return
         except Exception:
             pass