diff --git a/indra/newview/llappviewer.cpp b/indra/newview/llappviewer.cpp
index db2db43ee1bf655f2bae115aee47fc02f2ce0b7e..1bba17dc29f691042e853ece181446489c5662eb 100644
--- a/indra/newview/llappviewer.cpp
+++ b/indra/newview/llappviewer.cpp
@@ -4610,6 +4610,9 @@ void LLAppViewer::idle()
 	LLFrameTimer::updateFrameTime();
 	LLFrameTimer::updateFrameCount();
 	LLEventTimer::updateClass();
+	// LLApp::stepFrame() performs the above three calls plus mRunner.run().
+	// Not sure why we don't call stepFrame() here, except that LLRunner seems
+	// completely redundant with LLEventTimer.
 	LLNotificationsUI::LLToast::updateClass();
 	LLSmoothInterpolation::updateInterpolants();
 	LLMortician::updateClass();