Rails convert updated_at to rfc3339 format

I'm trying to convert the standard rails DB fields created_at and updated_at into the atom feed rfc3339 format. So far I have tried: ``` DateTime.rfc3339(issue.updated_at) ``` and ``` DateTime.parse(issue.updated_at).rfc3339 ``` and both times I get: ``` no implicit conversion of ActiveSupport::TimeWithZone into String ``` If I try and validate my atom feed at w3.org I get the following message: ``` updated must be an RFC-3339 date-time: 2013-06-27 13:42:34 UTC ``` The above error is for all the database updated_at fields. When I create the feed updated at field like the following I get no error: ``` xml.updated(Time.now.xmlschema) ``` I've searched high and low without fixing this issue. I did find Convert db date to rfc3339 but that didn't work for me. Any ideas?