diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 41e7746305..4bfe42f9bf 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -195,7 +195,9 @@ async def check_state_independent_auth_rules(
             for event_id in prev_state_events_ids
             if not batched_auth_events or event_id not in batched_auth_events
         }
-        # Try to load the `prev _state_events` from `batched_auth_events` initially
+        # We need to do some checks on the events provided as prev_state_events, so we need to load them.
+        # Try to load the `prev_state_events` from `batched_auth_events` initially as that can save us
+        # a database hit.
         prev_state_events = (
             {}
             if not batched_auth_events
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index ef60f252e5..8920eef3e6 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -198,6 +198,7 @@ class EventBuilder:
         if auth_event_ids is None:
             # Every non-create event must have a room ID
             assert self.room_id is not None
+            assert not self.room_version.msc4242_state_dags
             state_ids = await self._state.compute_state_after_events(
                 self.room_id,
                 prev_event_ids,
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 99ddb2d7b8..f09de7ccb4 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -642,7 +642,7 @@ class EventCreationHandler:
 
             prev_state_events:
                 The state event IDs which represent the current forward extremities of the state DAG.
-                Only applicable on room versions which use a state DAG.
+                Only applicable on room versions which use a state DAG (MSC4242).
 
         Raises:
             ResourceLimitError if server is blocked to some resource being
@@ -1003,7 +1003,7 @@ class EventCreationHandler:
                 based on the prev_events.
             prev_state_events:
                 The state event IDs which represent the current forward extremities of the state DAG.
-                Only applicable on room versions which use a state DAG.
+                Only applicable on room versions which use a state DAG (MSC4242).
         Returns:
             The event, and its stream ordering (if deduplication happened,
             the previous, duplicate event).
@@ -1281,8 +1281,8 @@ class EventCreationHandler:
 
             prev_state_events:
                 The state event IDs which represent the current forward extremities of the state DAG.
-                Only applicable on room versions which use a state DAG. If unset, populates them
-                from the current state dag forward extremities.
+                Only applicable on room versions which use a state DAG (MSC4242).
+                If unset, populates them from the current state dag forward extremities.
 
         Returns:
             Tuple of created event, UnpersistedEventContext
diff --git a/synapse/storage/controllers/persist_events.py b/synapse/storage/controllers/persist_events.py
index d040fbf671..be742661be 100644
--- a/synapse/storage/controllers/persist_events.py
+++ b/synapse/storage/controllers/persist_events.py
@@ -1034,7 +1034,7 @@ class EventsPersistenceStorageController:
                 **{SERVER_NAME_LABEL: self.server_name}
             ).observe(len(result))
 
-        # There should always be at least one forward extremity. 
+        # There should always be at least one forward extremity.
         assert result, f"No state dag forward extremities left in room {room_id}!"
         return result