diff --git a/index.html b/index.html
index c071afe..494b8fc 100644
--- a/index.html
+++ b/index.html
@@ -112,6 +112,7 @@ var _COLOR_GRASS = '#388E3C',
   }
 
   function drawBracket() {
+    if(bVec != null) return;
     var x = pX,
         y = pY
     if(Math.hypot(pX - bX, pY - bY) > _MAX_BRACKET){