diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 68e724ac7f..7ad2198d96 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -36,6 +36,8 @@ RoomsForUser = namedtuple(
 )
 
 
+# We store this using a namedtuple so that we save about 3x space over using a
+# dict.
 ProfileInfo = namedtuple(
     "ProfileInfo", ("avatar_url", "display_name")
 )