MS Access – Form with subforms.

I have a form with 2 subforms. After I enter/update a record and tab through the subform fields, the next time I enter the subform the cursor is on the last field. I then have to arrow back through the previous fields on the subform to get to the first field. How can I make it default to the first field of the subform.
Thanks in advance for any help you can give me.
Penny