How to make Active Record join return unique objects?

I have a simple query need: Find a list of users who made an order since Jan 1, 2013.

In SQL, it's a very simple query.

But I'm using Rails and Active Record.

So I wrote: User.joins(:orders).where("orders.created_at >= '2013-01-01 00:00:00'")

In our database, we have 100 orders made since 01/01/2013 by 75 users. (Some users made more than one order apparently.)

However, the expression above returns 100 users. (There must be duplicates.)

I tried User.joins(:orders).where("orders.created_at >= '2013-01-01 00:00:00'").uniq

That doesn't work either.

How can I get the 75 users who've made an order since 01/01/2013?