diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index dd4ca74ba..9c7dcdba9 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -419,6 +419,8 @@ class FederationServer(FederationBase):
                         min_depth=min_depth,
                     )
 
+                    # We want to sort these by depth so we process them and
+                    # tell clients about them in order.
                     missing_events.sort(key=lambda x: x.depth)
 
                     for e in missing_events: