1 files changed, 3 insertions, 2 deletions
diff --git a/synapse/handlers/read_marker.py b/synapse/handlers/read_marker.py
index 800240b8a9..3f46a16b90 100644
--- a/synapse/handlers/read_marker.py
+++ b/synapse/handlers/read_marker.py
@@ -48,9 +48,10 @@ class ReadMarkerHandler(BaseHandler):
             should_update = True
 
             if existing_read_marker:
+                # Only update if the new marker is ahead in the stream
                 should_update = yield self.store.is_event_after(
-                    existing_read_marker['marker'],
-                    event_id
+                    event_id,
+                    existing_read_marker['marker']
                 )
 
             if should_update: