It has been confirmed by DataMapper’s core developer Martin Gamsjaeger (snusnu) that it is a bug. In short, created_[at|on] can be manually overridden, but updated_[at|on] cannot. The workaround is simple, do it in two steps, for example: job = Job.create( title: "Web Developer", created_at: Time.now - 2 ) job.update!(updated_at: Time.now - 1) Please check the bug ticket to see when it’s getting fixed.