diff --git a/routes/billing.js b/routes/billing.js
index 57275b9..998440f 100644
--- a/routes/billing.js
+++ b/routes/billing.js
@@ -216,6 +216,12 @@ router.get('/export/csv', requireAdmin, async (req, res) => {
       ORDER BY m.last_name ASC
     `, [period]);
 
+    // Alle offenen Rechnungen dieser Periode als bezahlt markieren
+    await db.query(
+      "UPDATE invoices SET status='paid', paid_at=NOW() WHERE period=? AND status='open'",
+      [period]
+    );
+
     res.setHeader('Content-Type', 'text/csv; charset=utf-8');
     res.setHeader('Content-Disposition', `attachment; filename="SEPA_${period}.csv"`);