diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 33fccfa7a8..dd28c2efe3 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -386,11 +386,18 @@ class EventsStore(SQLBaseStore):
                                 if all_single_prev_not_state:
                                     continue
 
-                            state = yield self._calculate_state_delta(
-                                room_id, ev_ctx_rm, new_latest_event_ids
+                            logger.info(
+                                "Calculating state delta for room %s", room_id,
                             )
-                            if state:
-                                current_state_for_room[room_id] = state
+                            current_state = yield self._get_new_state_after_events(
+                                ev_ctx_rm, new_latest_event_ids,
+                            )
+                            if current_state is not None:
+                                delta = yield self._calculate_state_delta(
+                                    room_id, current_state,
+                                )
+                                if delta is not None:
+                                    current_state_for_room[room_id] = delta
 
                 yield self.runInteraction(
                     "persist_events",
@@ -467,20 +474,22 @@ class EventsStore(SQLBaseStore):
         defer.returnValue(new_latest_event_ids)
 
     @defer.inlineCallbacks
-    def _calculate_state_delta(self, room_id, events_context, new_latest_event_ids):
-        """Calculate the new state deltas for a room.
+    def _get_new_state_after_events(self, events_context, new_latest_event_ids):
+        """Calculate the current state dict after adding some new events to
+        a room
 
-        Assumes that we are only persisting events for one room at a time.
+        Args:
+            events_context (list[(EventBase, EventContext)]):
+                events and contexts which are being added to the room
+
+            new_latest_event_ids (iterable[str]):
+                the new forward extremities for the room.
 
         Returns:
-            3-tuple (to_delete, to_insert, new_state) where both are state dicts,
-            i.e. (type, state_key) -> event_id. `to_delete` are the entries to
-            first be deleted from current_state_events, `to_insert` are entries
-            to insert. `new_state` is the full set of state.
-            May return None if there are no changes to be applied.
+            Deferred[dict[(str,str), str]|None]:
+                None if there are no changes to the room state, or
+                a dict of (type, state_key) -> event_id].
         """
-        # Now we need to work out the different state sets for
-        # each state extremities
         state_sets = []
         state_groups = set()
         missing_event_ids = []
@@ -523,12 +532,12 @@ class EventsStore(SQLBaseStore):
                 state_sets.extend(group_to_state.itervalues())
 
         if not new_latest_event_ids:
-            current_state = {}
+            defer.returnValue({})
         elif was_updated:
             if len(state_sets) == 1:
                 # If there is only one state set, then we know what the current
                 # state is.
-                current_state = state_sets[0]
+                defer.returnValue(state_sets[0])
             else:
                 # We work out the current state by passing the state sets to the
                 # state resolution algorithm. It may ask for some events, including
@@ -537,8 +546,7 @@ class EventsStore(SQLBaseStore):
                 # up in the db.
 
                 logger.info(
-                    "Resolving state for %s with %i state sets",
-                    room_id, len(state_sets),
+                    "Resolving state with %i state sets", len(state_sets),
                 )
 
                 events_map = {ev.event_id: ev for ev, _ in events_context}
@@ -567,9 +575,22 @@ class EventsStore(SQLBaseStore):
                     state_sets,
                     state_map_factory=get_events,
                 )
+                defer.returnValue(current_state)
         else:
             return
 
+    @defer.inlineCallbacks
+    def _calculate_state_delta(self, room_id, current_state):
+        """Calculate the new state deltas for a room.
+
+        Assumes that we are only persisting events for one room at a time.
+
+        Returns:
+            3-tuple (to_delete, to_insert, new_state) where both are state dicts,
+            i.e. (type, state_key) -> event_id. `to_delete` are the entries to
+            first be deleted from current_state_events, `to_insert` are entries
+            to insert. `new_state` is the full set of state.
+        """
         existing_state = yield self.get_current_state_ids(room_id)
 
         existing_events = set(existing_state.itervalues())