diff --git a/setra_client/models.py b/setra_client/models.py
index 3b96a03cb644c65027105d2086570b32ef824d63..4f32b6583c94b5bfa0a3f0d9fac3b99a7b173783 100644
--- a/setra_client/models.py
+++ b/setra_client/models.py
@@ -79,7 +79,7 @@ class InputBatch(BaseModel):
 
     client: str
     batchid: str
-    period: int
+    period: Optional[int]
     interface: str
     vouchertype: str
     vouchers: List[Voucher]