diff --git a/synapse/state.py b/synapse/state.py
index 18f1edef42..4c8247e7c2 100644
--- a/synapse/state.py
+++ b/synapse/state.py
@@ -147,6 +147,19 @@ class StateHandler(object):
 
     @defer.inlineCallbacks
     def get_current_state_ids(self, room_id, latest_event_ids=None):
+        """Get the current state, or the state at a set of events, for a room
+
+        Args:
+            room_id (str):
+
+            latest_event_ids (iterable[str]|None): if given, the forward
+                extremities to resolve. If None, we look them up from the
+                database (via a cache)
+
+        Returns:
+            Deferred[dict[(str, str), str)]]: the state dict, mapping from
+                (event_type, state_key) -> event_id
+        """
         if not latest_event_ids:
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)