Close Quarters Fighting

 
Prerequisite(s): Base Attack Bonus 3+
 
Benefit: Any damage you inflict with an attack of opportunity provoked by a grapple attempt is added to your ensuing grapple check. You are entitled to make an attack of opportunity even if the attacking creature has Improved Grab. This feat does not provide you with additional attacks of opportunity in a round.
 
Source: Complete Warrior, Draconomicon