diff --git a/synapse/storage/schema/delta/56/room_key_hash.sql b/synapse/storage/schema/delta/56/room_key_hash.sql
index fa61cd3ff0..be2a559b6e 100644
--- a/synapse/storage/schema/delta/56/room_key_hash.sql
+++ b/synapse/storage/schema/delta/56/room_key_hash.sql
@@ -14,4 +14,4 @@
  */
 
 -- store the current hash of backup version
-ALTER TABLE e2e_room_keys_versions ADD COLUMN hash TEXT NULLABLE;
+ALTER TABLE e2e_room_keys_versions ADD COLUMN hash TEXT;