Substract 1 month to update table SQL Server

I need to update all the issuedat (date field) to be less than one month from the column paidat (date field)

ex:

if paidat = 01/02/2011 then issuedat should开发者_运维知识库 = 01/01/2011

UPDATE invoices SET invoices.issuedat = ????

UPDATE invoices SET invoices.issuedat = dateadd(MM,-1,paidat)