diff --git a/src/pretix/plugins/banktransfer/tasks.py b/src/pretix/plugins/banktransfer/tasks.py
index 1e85c252b3..d11eb1f50b 100644
--- a/src/pretix/plugins/banktransfer/tasks.py
+++ b/src/pretix/plugins/banktransfer/tasks.py
@@ -44,7 +44,7 @@ def _handle_transaction(event: Event, trans: BankTransaction, code: str):
         try:
             mark_order_paid(trans.order, provider='banktransfer', info=json.dumps({
                 'reference': trans.reference,
-                'date': trans.date.isoformat(),
+                'date': trans.date,
                 'payer': trans.payer,
                 'trans_id': trans.pk
             }))