diff --git a/assets/js/sumorobot.js b/assets/js/sumorobot.js
index cae8663..3476997 100755
--- a/assets/js/sumorobot.js
+++ b/assets/js/sumorobot.js
@@ -529,7 +529,7 @@ window.onload = function() {
     /* stop button listener */
     $(".btn-stop").click(function() {
         sumostart = false;
-        sumorobot.send('{"to": "sumo-' + robotId + '@00000514", "cmd': 'stop'}");
+        sumorobot.send('{"to": "sumo-' + robotId + '@00000514", "cmd": "stop"}');
         workspace.highlightBlock(lastHighlighted, false);
     });