help with update query!

I have two tables... BillD and NewBillD

BillD has columns [order number], [price], [cost] etc.

NewBillD has just columns [order number], [price]

the order numbers in both tables are the same. I want to update billd with price from NewBillD.

Why will this query not work:

Update billd
set price = newbilld.price
where account = newbilld.account

Thanks!

Kenduh, forgot to join... Is it Friday yet?