If there is a zero in box 2a, it seems that what was inherited was an account in an employer plan, not an IRA, which was subsequently rolled over to an inherited IRA. In such a case, the Form 1099-R provided by the payer and the form should have codes 4 and G in box 7 and the IRA/SEP/SIMPLE box unmarked (or codes 4 and H if the account was a Roth account). The entry of such a Form 1099-R does not add to taxable income. The amount would be included on Form 1040 line 5a but excluded from line 5b.
If the Form 1099-R instead has the IRA/SEP/SIMPLE box marked (or code T or Q in box 7) indicating a distribution from an IRA, the Form 1099-R reports a distribution paid to you that was not eligible for deposit into an inherited IRA as a rollover. Non-spouse beneficiaries are not permitted to roll over distributions from inherited IRAs.
