--- a/src/client.py
+++ b/src/client.py
@@ -5,9 +5,11 @@ def sync(feed, page_size=50):
     """Retrieve every event from the feed exactly once, oldest first."""
     events = []
     after_ts = None
+    after_id = None
     while True:
-        batch = feed.fetch(after_ts=after_ts, limit=page_size)
+        batch = feed.fetch(after_ts=after_ts, after_id=after_id, limit=page_size)
         if not batch:
             return events
         events.extend(batch)
         after_ts = batch[-1].ts
+        after_id = batch[-1].id