Instructions for Form 8991 Part II—Modified Taxable Income, line 3a should read:
Enter the amount of taxable income after any net operating loss and special deductions.
If the current year reports a loss, without any net operating loss carryovers, the amount entered here may be less than zero.
If the current year reports taxable income and there is a net operating loss carryover that would reduce taxable income below zero, enter “-0-.” Do not enter an amount less than zero.