diff --git a/scrapy/signals.py b/scrapy/signals.py
index 6b9125302..cd7ed7fb1 100644
--- a/scrapy/signals.py
+++ b/scrapy/signals.py
@@ -14,6 +14,7 @@ spider_error = object()
 request_scheduled = object()
 request_dropped = object()
 request_reached_downloader = object()
+request_left_downloader = object()
 response_received = object()
 response_downloaded = object()
 item_scraped = object()