Pending sales of previously owned U.S. homes rose slightly in May, the fourth straight monthly gain, a real estate trade group said on Wednesday.

The National Association of Realtors said its Pending Home Sales Index, based on contracts signed in May, was up 0.1 percent to 90.7 from a upwardly revised index of 90.6 in April. The index for April had previously been reported as 90.3.

Economists polled by Reuters ahead of the report were expecting pending home sales to remain unchanged. The trade group said April's gain was revised upward to 7.1 percent from the 6.7 percent previously reported.