How report interest income without a 1099-INT form on Turbotax?

A relative passed away and the executor of the estate sent me, the beneficiary,  a U.S. Treasury refund check with interest. I assume that I have to report the interest, but I have not received a Form 1099-INT. Some people on this forum have said to report the amount of interest in TurboTax the same as if I had received a 1099-INT from a bank.  I did this and indicated the amount of interest in Box 1 and entered the payer's name as "U.S. Treasury."  However, TurboTax flagged this, saying it needs a Federal Identification number (FEIN).  How do I report the interest without the number?