diff --git a/src/newsreader/news/collection/feed.py b/src/newsreader/news/collection/feed.py
index 2ac4854..09acac0 100644
--- a/src/newsreader/news/collection/feed.py
+++ b/src/newsreader/news/collection/feed.py
@@ -188,13 +188,13 @@ class FeedDuplicateHandler:
             "publication_date": post.publication_date,
         }
 
-        for existing_post in self.queryset.order_by("-publication_date")[:50]:
+        for existing_post in self.queryset.order_by("-publication_date")[:500]:
             if self.is_duplicate(existing_post, values):
                 return True
 
     def is_duplicate(self, existing_post: Post, values: Dict) -> bool:
         for key, value in values.items():
-            existing_value = getattr(existing_post, key, object())
+            existing_value = getattr(existing_post, key, None)
             if existing_value != value:
                 return False