Buy one Get one item price determination

We have a promotional modifier to give a free item and the B1G1 item is setup with 100% discount (Application method=% and Value=100).  This works fine and the item is priced at 0.

However when the customer is given an additional discount at the Order level, the B1G1 item price is going into negative. This is not desired, the free item should always be priced at 0.

Is there a way to achieve this?

Thanks in advance.