diff --git a/facturier/management/commands/cleanup_transactionevents.py b/facturier/management/commands/cleanup_transactionevents.py
index b426f0d..a862b61 100644
--- a/facturier/management/commands/cleanup_transactionevents.py
+++ b/facturier/management/commands/cleanup_transactionevents.py
@@ -14,4 +14,4 @@ class Command(BaseCommand):
                 TransactionEvent.objects.create(transaction_id=event.transaction_id,
                                                 status='CANCELED',
                                                 invoice_id=event.invoice_id, regie=event.regie,
-                                                details='%s canceled because expired' % event.transaction_id)
+                                                details='{"message": "%s canceled because expired"}' % event.transaction_id)