postgresql unpivot

Given a monthly currency conversion table like:

iso4127_code	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
JPY	0.009613	0.009792	0.009778	0.009757	0.009827	0.009790	0.009829	0.009717	0.009346	0.009262	0.008606	0.008375

I need to unpivot so that I get a table that is:

iso4127_code	month	rate
JPY	1	0.009613
JPY	2	0.009792
...

select iso4127_code, 
unnest(array[1,2,3,4,5,6,7,8,9,10,11,12]) as month,
unnest(array[jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec]) as rate
from table