diff --git a/synapse/storage/schema/full_schemas/16/event_edges.sql b/synapse/storage/schema/full_schemas/16/event_edges.sql
index 52eec883576be26ed8a0e6d40fda36294e855f15..6b5a5a88fae181557b726ab17e3cbb33a03457b1 100644
--- a/synapse/storage/schema/full_schemas/16/event_edges.sql
+++ b/synapse/storage/schema/full_schemas/16/event_edges.sql
@@ -37,7 +37,8 @@ CREATE TABLE IF NOT EXISTS event_edges(
     event_id TEXT NOT NULL,
     prev_event_id TEXT NOT NULL,
     room_id TEXT NOT NULL,
-    is_state BOOL NOT NULL,
+    is_state BOOL NOT NULL,  -- true if this is a prev_state edge rather than a regular
+                             -- event dag edge.
     UNIQUE (event_id, prev_event_id, room_id, is_state)
 );