Can't see Generate Gradle build files when migrating from Eclipse to Android Studio

I tried the instructions listed here http://developer.android.com/sdk/installing/migrate.html#Export, including upgrading my adt plugin (I simply checked for updates in Eclipse, per http://developer.android.com/tools/help/adt.html#Updating ; it said I was up to date). But when I tried to export projects from Eclipse I don't see the "Generate Gradle build files" option, only "Export Android Application."

enter image description here

Is there something more that I have to do to see this option? I am using the Android Developer Tools version for Mac, Build: v21.1.0-569685.

Solution

It turns out that I can't just check for updates like the developer's site said for the ADT: I still have ADT version 21. Reinstalling ADT works.

This question has some useful info on updating to ADT 22 Can't update Eclipse ADT to 22.