McDonald’s mcd is tweaking its iconic Big Mac sandwich in the hopes of sparking new interest in the 50-year sandwich icon.

The fast-food chain said on Thursday it is introducing both a smaller and a larger Big Mac nationwide for a limited time early next year after a successful test in some markets. The move is a rare expansion of the classic menu item. One new version of the sandwich, called the Grand Mac, will have two all-beef patties weighing one-third of a pound. The other, dubbed Mac Jr., will shrink the sandwich down to have only a single patty and no middle bun.

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McDonald’s tested the new Big Macs in Columbus, Ohio and Dallas-Fort Worth earlier this year.

“We listened to our customers, who told us they wanted different ways to enjoy the one-of-a-kind Big Mac taste,” McDonald’s chef Mike Haracz said in a statement.

The current Big Mac has one-fifth of a pound of beef. McDonald’s first introduced the Big Mac in 1967, and the signature sandwich has barely changed since then.

The expansion is the latest move by McDonald’s, whose U.S. comparable sales have risen for several quarters after a deep slump in recent years. In its most recent fiscal quarter, sales at established restaurants rose 1.3%, helped by the return of McDonald’s popular All Day Breakfast, and promotions like its McPick 2 offer and the launch of Chicken McNuggets with no artificial preservatives. Still, that growth was below McDonald’s pace in preceding quarters. McDonald’s shares closed at $111.72 on Thursday, down from a recent all-time high of $131.96.

McDonald’s long time supremacy in the burger wars has come under fire in recent years by the emergence of such chains as Shake Shack and In-N-Out.