diff --git a/layout/xul/base/test/test_bug511075.html b/layout/xul/base/test/test_bug511075.html
index 3fadb53ce9b1..313d140a3708 100644
--- a/layout/xul/base/test/test_bug511075.html
+++ b/layout/xul/base/test/test_bug511075.html
@@ -68,6 +68,7 @@ var tests = [
     synthesizeMouse(scroller, x, y, { type: "mouseup" }, window);
   },
   function() {
+    scroller.onscroll = null;
     ok(true, "Clicking the scrollbar should scroll");
     finish();
   }