diff --git a/archiver/links.py b/archiver/links.py
index 990df953..a16ca594 100644
--- a/archiver/links.py
+++ b/archiver/links.py
@@ -80,8 +80,8 @@ def new_links(all_links, existing_links):
     This is used to determine which links are new and not indexed jet. Set the
     ONLY_NEW environment variable to activate this filter mechanism.
     """
-    existing_urls = list(map(lambda l: l['url'], existing_links))
-    return list(filter(lambda l: l['url'] not in existing_urls, all_links))
+    existing_urls = {link['url'] for link in existing_links}
+    return [link for link in all_links if link['url'] not in existing_urls]
 
 def archivable_links(links):
     """remove chrome://, about:// or other schemed links that cant be archived"""