You can make a parry and riposte against an opponent who attempts to cast a spell.

Prerequisite(s): Int 15, Spellcraft 3 ranks, 5th-level duelist

Benefit: When you have elected to reserve one of your attacks to make a parry attempt, if an opponent within reach attempts to cast a spell, you can use your parry to attempt to parry the spell. You make a parry attack roll with a -4 penalty opposed by the opponent's concentration check. If your roll is Greater than the caster's concentration check, the opponent loses the spell, and you can make a riposte against the caster. You can attempt to parry even if your opponent successfully casts defensively.

Normal: Normally you can only parry and riposte attacks made against you.