--- a/dom/webidl/EventHandler.webidl
+++ b/dom/webidl/EventHandler.webidl
@@ -117,16 +117,17 @@ interface GlobalEventHandlers {
            attribute EventHandler onlostpointercapture;
 
            // Mozilla-specific handlers. Unprefixed handlers live in
            // Document rather than here.
            attribute EventHandler onmozfullscreenchange;
            attribute EventHandler onmozfullscreenerror;
 
            // CSS-Animation and CSS-Transition handlers.
+           attribute EventHandler onanimationcancel;
            attribute EventHandler onanimationend;
            attribute EventHandler onanimationiteration;
            attribute EventHandler onanimationstart;
            attribute EventHandler ontransitioncancel;
            attribute EventHandler ontransitionend;
            attribute EventHandler ontransitionrun;
            attribute EventHandler ontransitionstart;