diff --git a/src/github.com/matrix-org/dendrite/syncapi/storage/account_data_table.go b/src/github.com/matrix-org/dendrite/syncapi/storage/account_data_table.go
index c51cfd19a..1668d995f 100644
--- a/src/github.com/matrix-org/dendrite/syncapi/storage/account_data_table.go
+++ b/src/github.com/matrix-org/dendrite/syncapi/storage/account_data_table.go
@@ -37,6 +37,8 @@ CREATE TABLE IF NOT EXISTS account_data_type (
     -- We don't want two entries of the same type for the same user
     CONSTRAINT account_data_unique UNIQUE (user_id, room_id, type)
 );
+
+CREATE UNIQUE INDEX IF NOT EXISTS account_data_id_idx ON account_data(id);
 `
 
 const insertAccountDataSQL = "" +