diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 6d2aae9c4a..eb8bbe13ab 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -631,6 +631,24 @@ class EventsStore(EventsWorkerStore):
         if old_state_groups == new_state_groups:
             defer.returnValue((None, None))
 
+        if len(new_state_groups) == 1:
+            # If there is only one state group, then we know what the current
+            # state is.
+            if len(old_state_groups) == 1:
+                new_state_group = next(iter(new_state_groups))
+                old_state_group = next(iter(old_state_groups))
+
+                delta_ids = state_group_deltas.get(
+                    (old_state_group, new_state_group,), None
+                )
+                if delta_ids is not None:
+                    # We have a delta from the existing to new current state,
+                    # so lets just return that. If we happen to already have
+                    # the current state in memory then lets also return that,
+                    # but it doesn't matter if we don't.
+                    new_state = state_groups_map.get(new_state_group)
+                    defer.returnValue((new_state, delta_ids))
+
         # Now that we have calculated new_state_groups we need to get
         # their state IDs so we can resolve to a single state set.
         missing_state = new_state_groups - set(state_groups_map)
@@ -639,19 +657,7 @@ class EventsStore(EventsWorkerStore):
             state_groups_map.update(group_to_state)
 
         if len(new_state_groups) == 1:
-            # If there is only one state group, then we know what the current
-            # state is.
-            new_state_group = new_state_groups.pop()
-
-            delta_ids = None
-            if len(old_state_groups) == 1:
-                old_state_group = old_state_groups.pop()
-
-                delta_ids = state_group_deltas.get(
-                    (old_state_group, new_state_group,), None
-                )
-
-            defer.returnValue((state_groups_map[new_state_group], delta_ids))
+            defer.returnValue((state_groups_map[new_state_groups.pop()], None))
 
         # Ok, we need to defer to the state handler to resolve our state sets.