You have a higher AMT basis in the stock that was sold, compared to your regular tax basis. As TaxMaster stated, that should result in a lower tentative minimum tax vs your regular tax, and your AMT credit will come into play. That "adjustment" should be that additional AMT basis you have in the ISO shares you sold. This all can go horribly wrong if the sales price of the ISO shares ends up being less than the FMV at the time of the ISO exercise. The MTC can get "stuck".