Howto turn an integer into an interval?

Hi List,

I got a table named foobar with two fields

last_sms         is a 'timestamp without timezone'
resend_interval is a 'integer'

I choose 'integer' for resend_interval rather than a 'interval' because 
the frontend can easier handle the number of seconds. But now I'm stuck 
with the query to get all rows that we're older than 'resend_interval' 
in seconds.

My first try was:

SELECT *  FROM sms_groups  WHERE    (current_timestamp - last_sms) > '3600 seconds'::interval

This is working great and returns all rows that are older than a hour. 
But how I do this with the colum 'resend_interval' in the query?

SELECT *  FROM sms_groups  WHERE    (current_timestamp - last_sms) > resend_interval::interval

gives me only a "cannot cast type integer to interval". So how can I 
turn an integer to an interval? Or is there an other solution? 
Suggestions?

P.S: I'm using psql '7.4.5' of gentoo.

-- 
So long... Fuzz