diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index f3a056110..390647540 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -448,7 +448,7 @@ class Filter(object):
         """Returns a new filter with the given room IDs appended.
 
         Args:
-            room_ids (list): A list of room_ids.
+            room_ids (iterable[unicode]): The room_ids to add
 
         Returns:
             filter: A new filter including the given rooms and the old
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index 75c26fe06..49c439313 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -52,7 +52,7 @@ class SearchHandler(BaseHandler):
             room_id (str): id of the room to search through.
 
         Returns:
-            Deferred[iterable[str]]: predecessor room ids
+            Deferred[iterable[unicode]]: predecessor room ids
         """
 
         historical_room_ids = []
diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index c02130d9d..c3ab7db7a 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -446,7 +446,7 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
             room_id (str)
 
         Returns:
-            Deferred[str]: predecessor room id
+            Deferred[unicode|None]: predecessor room id
         """
         state_ids = yield self.get_current_state_ids(room_id)
         create_id = state_ids.get((EventTypes.Create, ""))