Block unit of feet in an inches dwg

I have a drawing created by someone else that was drawn in inches, as we do, but
the Block Unit is set to feet, so when I XREF it into my drawing it scales
itself up by 12 automatically.

How can I change the Block Unit setting in the original drawing to be inches?
I've looked through all the system variables in that drawing but could find
nothing that controls the Block Unit of the drawing itself. I can control how
blocks are inserted into that drawing are handled, but not for the drawing to be
inserted into another drawing.

Thanks for any clues,