KFC has issued an apology after its app sent users in Germany a message encouraging them to commemorate Kristallnacht with fried chicken. The Nazi attacks on Jewish homes, businesses, and synagogues beginning on Nov. 9, 1938 left at least 91 people dead and is broadly considered the start of the Holocaust. The horrific event—also known as the Night of Broken Glass—is marked every year in Germany. KFC said “an error in our system” was responsible for the message sent Wednesday, which read: “It’s memorial day for Kristallnacht! Treat yourself with more tender cheese on your crispy chicken. Now at KFCheese!” Another message apologizing for the mistake was sent about an hour later, according to local media reports. In a statement to Newsweek, KFC explained that the “automated push notification” was “linked to calendars that include national observances.” The company added an apology for the “unplanned, insensitive and unacceptable message.”