Theme parks are moving to offer free return tickets when temperatures hit extreme levels, a sign that operators are concerned worsening heat waves may deter customers and hurt attendance.

SeaWorld Entertainment Inc. expanded its weather guarantee policy to cover heat indexes above 110 at its three US locations, according to a statement Wednesday. It’s the first major American theme park to do so, according to a review of cancellation policies by Bloomberg, and comes as this year looks to become the hottest in recent history following a record-breaking July.

“They’ve laid down a blueprint that I think has been a gray area for a lot of park operators and, obviously, this has become a bigger issue,” Truist Securities analyst Michael Swartz said in an interview.

SeaWorld’s shares are down about 11% this month after attendance slumped in the second quarter. Its new heat policy is likely a strategy to increase foot traffic as weather impacts operations, Swartz said.

The cities where SeaWorld’s US locations operate — Orlando, San Diego and San Antonio — hit a heat index of 110 or higher 13 times in the past year, according to an analysis of National Oceanic and Atmospheric Administration data by Bloomberg. San Antonio reached 110 or higher nine times, Orlando four, and San Diego zero.

SeaWorld said its new policy is “the most generous inclement weather policy in the industry.” No other major US theme parks explicitly offer free return tickets in cases of extreme heat, according to a review of policies by Bloomberg. Most, like Walt Disney World Co. and Six Flags Entertainment Corp., limit their cancellation policies to hurricanes or storms. Cedar Fair LP doesn’t offer rain checks, according to its website.