A French museum discovered half its collection is forged.

A museum in Elne, France, devoted to the painter Étienne Terrus said that 82 works from the institution’s collection purportedly by the artist are actually fakes, NPR reported. The forgiers were discovered by an outside curator who noticed that several works attributed to Terrus portrayed buildings that were built decades after the artist’s death in 1922. Further investigation found that other works had clearly been made by imposters rather than Terrus, a well-known landscape painter who was friends with Henri Matisse. “There are several types of fakes in the collection,” the outside curator, Eric Forcada, told NPR in a translated statement. “There are some that were taken and just signed posteriorly with Terrus’ name, and others that were made expressly to look like Terrus’ work.”

The remaining 52 works attributed Terrus in the collection have been authenticated, and the town has pledged to track down the forgers. And the museum’s shocking discovery could prompt similar investigations at other regional institutions, the collections of which are largely comprised of locally known artists whose work is low hanging fruit for forgers.