diff --git a/roles/custom/matrix-synapse/defaults/main.yml b/roles/custom/matrix-synapse/defaults/main.yml
index b45381c56..657d546bf 100644
--- a/roles/custom/matrix-synapse/defaults/main.yml
+++ b/roles/custom/matrix-synapse/defaults/main.yml
@@ -1456,7 +1456,7 @@ matrix_synapse_redaction_retention_period: 7d
 # Controls how long to keep locally forgotten rooms before purging them from the DB.
 # Defaults to `null`, meaning it's disabled.
 # Example value: 28d
-matrix_synapse_forgotten_room_retention_period: ~
+matrix_synapse_forgotten_room_retention_period: 28d
 
 matrix_synapse_user_ips_max_age: 28d