diff --git a/src/js/buttons.js b/src/js/buttons.js
index 731312f..6e7d295 100644
--- a/src/js/buttons.js
+++ b/src/js/buttons.js
@@ -14,7 +14,7 @@ function Buttons(session) {
 
 	document.addEventListener('keydown', function(event) {
 		var button = session.get('options').layout[event.key];
-		if(button != undefined && mapping[button] != undefined) {
+		if(button != undefined && mapping != undefined && mapping[button] != undefined) {
 			event.preventDefault();
 			mapping[button]();
 		}