Red Robin has announced it will be selling a limited number of $20 passes entitling holders to a free burger and side every day in May.

The Bottomless Burger Pass will go on sale at 9 a.m. Mountain time on Thursday, according to the Colorado-based chain’s website.

That means it will be available at 8 a.m. Pacific time, but most likely only for a very short time.

Red Robin cautions the passes could sell out in minutes, and usually in these kinds of promotions that advice is reliable.

The reason for the promotion is National Hamburger Month, which is in May.

Specifically, the pass is good for one Gourmet Burger and a standard Bottomless Side a day. Premium sides or substitutions could cost extra, according to a news release.

Red Robin’s Gourmet Cheeseburger costs around $16.39.

Visit redrobin.com/national-burger-month for details.