Updating Orders From Customer Table

I want to update the orders that has invoice number empty when doing a change in the customer table Nm.

My order table is named order and customer is named customer, they both have a column named CustId and Nm (name).

This works fine and shows in my case column Nm in 4 rows (for orders);

select
Order.Nm
from
Order
Join Customer
on Order.CustId=Customer.CustId
where
Order.CustId=@variable and InvoNo=''

But the update statement gets error;

Update
Order
set
Order.Nm=Customer.Nm
from
Order
inner join Customer
on
Order.CustId=Customer.CustId
where
Ord.CustId=@Variable and InvoNo=''

I use SQL 2008....