S&P 500 index futures turned negative on Wednesday after an unexpected month-over-month decline in June durable goods orders.

New orders for long-lasting U.S. manufactured goods fell for a second straight month, posting their largest decline since August, according to a government report that was further evidence economic growth cooled in the second quarter.

S&P 500 futures fell 3.4 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures dropped 28 points and Nasdaq 100 futures shed 3.5 points.

(Reporting by Angela Moon; Editing by Padraic Cassidy)