If I understand correctly, your partner's employer issued him company stock and reported that as income. You then sold the stock and received a Form1099-B reporting the sale. If the cost basis on the 1099-B is zero, you will need to adjust it so that it is the same amount as the income reported on the Form 1099-B. Brokers typically report a zero cost basis when company stock is involved, requiring it to be adjusted when the sale is reported.
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