More than 175 years after his death, Frederic Chopin is still making people dance: an unknown waltz by the Polish composer was accidentally found in the storage of the Morgan Library-Museum in New York, according to the New York Times.

The score, which had “Waltz” written on it in French, was discovered by a conservator last spring.

“I wondered: What is going on here? What could this be?’ explained conservator Robinson McLellan, adding that he “didn’t recognize the music.”

At first he was not sure that this waltz was really a Chopin composition. He took a picture of the sheet music and played the piece on the piano he had at home. An expert from the University of Pennsylvania was then consulted, and the Morgan Library concluded that the waltz is authentic after examining the ink used and the paper it was written on.

The calligraphy corresponded to that of Chopin, such as a key of F and some bird carvings, characteristic of the genius composer who died in France in 1849.

“We are absolutely convinced of our conclusions,” Robinson McLellan told the paper.

According to the Morgan Library, the piece dates between 1830-35, when Chopin was around 20-25.