The Association of Gaming Equipment Manufacturers Index declined almost 2 percent in May, although the majority of the 13 companies making up the index saw share price gains.
The composite index fell to 196.98 in the latest period, which represents a decline of 3.70 points from April and is the second month-to-month decline this year.
Compared to a year ago, the AGEM Index is up 18.05 points, or 10.1 percent.
Eight of the 13 global gaming equipment suppliers saw their share prices rise, with four up by more than 10 percent.
These gains were offset by declines reported by five suppliers, two of which were down by more than 10 percent from the prior month.
Gaming supplier stocks underperformed the broader market indices with the Dow Jones Industrial Average, the Nasdaq and the S&P 500 all posting gains in the month.
Scientific Games Corporation was the biggest gainer, contributing 3.08 points due to a stock price gain of just over 20 percent.
On the downside, International Game Technology lost 11 percent, while Galaxy Gaming was down almost 11 percent.