diff --git a/js/pianos4.js b/js/pianos4.js
index 382c36f2bbbf6f3b79c7e4ab95033f7db85c3849..1229e1f2518cb745ee241c6e03ba6d872972c204 100644
--- a/js/pianos4.js
+++ b/js/pianos4.js
@@ -3300,10 +3300,8 @@ function Pianos4( params )
 
     var onTutorDataAvailable = function( what, data )
     {
-        if( !( what in tutorData ) )
-        	return;
-        
         log( 'Tutor data available: ' + what );
+        assert( !( what in tutorData ) );
         tutorData[ what ] = data;
         assert( Object.keys( tutorData ).length <= 2 );