diff --git a/morss/crawler.py b/morss/crawler.py
index 474db4b..54a7ce7 100644
--- a/morss/crawler.py
+++ b/morss/crawler.py
@@ -620,6 +620,7 @@ class BaseCache:
         self.trim()
 
         t = threading.Timer(delay, self.autotrim)
+        t.daemon = True
         t.start()
 
     def __contains__(self, url):