diff --git a/changelog.txt b/changelog.txt
index b8d5cd96..116f7cb3 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -15,7 +15,7 @@ OPENSEADRAGON CHANGELOG
 *     Button "onExit" changed to "exit"
 *     Button "onFocus" changed to "focus"
 *     Button "onBlur" changed to "blur"
-* BREAKING CHANGE: Button event handler method signatures changed to 'handlerMethod( eventSource, eventData)' (#224)
+* BREAKING CHANGE: Button event handler method signatures changed to 'handlerMethod( eventSource, eventData)' where eventData == { button } (#224)
 * MouseTracker now passes the original event objects to its handler methods (#23)
 * MouseTracker now supports an optional 'moveHandler' method for tracking mousemove events (#215)
 * Fixed: Element-relative mouse coordinates now correct if the element and/or page is scrolled (using new OpenSeadragon.getElementOffset() method) (#131)