Furniture tends to appreciate in value -- as time goes by. That explains why the piano used in the Oscar-winning classic movie “Casablanca” sold for more than $600,000 at auction today.

The upright piano went up on the Sotheby's auction block Friday in New York, where an unidentified buyer claimed it for $602,500.

The Japanese collector who bought the piano for $154,000 in 1988 from Sotheby's is hoping to turn a tidy profit on the tiny piano.

The piano is notable because it’s a cafe piano, designed to be wheeled from table to table, and has only 58 keys, 30 fewer than a conventional modern instrument.

The piano went missing for years but turned up in a prop-shop sale in the early 1980s. A Los Angeles-based collector spotted it and recognized its size and the shape, even though it was reportedly covered in 20 layers of paint.

Sure enough, when the collector checked the back, he discovered the Warner Brothers number and realized what he had found.

The famed piano appears in a flashback scene in Paris, when pianist Sam plays “As Time Goes By” during the love scene between in Humphrey Bogart's character, Rick, and Ingrid Bergman’s Ilsa.

“Here’s looking at you, kid,” Rick says, as the lovers toast each other with champagne in the film that has been named the most romantic and quotable movie of all time by the American Film Institute.

In reality, the actor playing Sam, Dooley Wilson, was not actually playing the instrument, which was one of two used in “Casablanca.” (Another piano was used in the Moroccan scenes.)

Instead, studio musician Elliot Carpenter played another piano just off camera while Dooley pretended to play, imitating Carpenter’s hand movements while he sang.

The piano was put up for auction on the film’s 70 anniversary.

With files from The Associated Press