diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index c7ef6d2a9c..4a7613b262 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -222,6 +222,7 @@ class ApplicationServicesHandler:
 
         # Notify appservices of updates in ephemeral event streams.
         # Only the following streams are currently supported.
+        # FIXME: We should use constants for these values.
         if stream_key not in (
             "typing_key",
             "receipt_key",
@@ -494,6 +495,8 @@ class ApplicationServicesHandler:
         # Filter out users that this appservice is not interested in
         users_appservice_is_interested_in: List[str] = []
         for user in users:
+            # FIXME: We should do this farther up the call stack. We currently repeat
+            #  this operation in _handle_presence.
             if isinstance(user, UserID):
                 user = user.to_string()