diff --git a/barker/barker/routers/voucher/show.py b/barker/barker/routers/voucher/show.py
index 1871c98..ca8b8c4 100644
--- a/barker/barker/routers/voucher/show.py
+++ b/barker/barker/routers/voucher/show.py
@@ -42,7 +42,7 @@ def from_bill(
         query = select(Voucher)
         if re.compile(r"^\d{1,3}-\d{1,4}$").match(id_):
             s, n = id_.split("-")
-            i = int(s * 10000) + int(n)
+            i = (int(s) * 10000) + int(n)
             query = query.where(Voucher.bill_id == i, Voucher.voucher_type == VoucherType.REGULAR_BILL)
         elif re.compile(r"^K-\d+$").match(id_):
             query = query.where(