diff --git a/pages/booking/[uuid]/bill.tsx b/pages/booking/[uuid]/bill.tsx
index 412df75..c2209c2 100644
--- a/pages/booking/[uuid]/bill.tsx
+++ b/pages/booking/[uuid]/bill.tsx
@@ -116,7 +116,7 @@ export default function BillPage({
   // in case the props change, update the internal state
   useEffect(() => setBooking(bookingProp), [bookingProp])
 
-  const onSubmit = async (event) => {
+  const onSubmit = async (event: React.FormEvent<HTMLFormElement>) => {
     event.preventDefault()
     const bill = await saveBill(booking, {
       milageStart,