diff --git a/js/main.js b/js/main.js
index 667afcc8..fb1411e9 100644
--- a/js/main.js
+++ b/js/main.js
@@ -414,7 +414,7 @@ var MM = (function() {
 		hideModule: function(module, speed, callback) {
 			hideModule(module, speed, function() {
 				module.hidden = true;
-				callback();
+				if (typeof callback === 'function') { callback(); }	
 			});
 		},