diff --git a/index.php b/index.php
index f3cb20a..b44bc8c 100644
--- a/index.php
+++ b/index.php
@@ -124,7 +124,7 @@
 
                     var drawing = false;
                     canvas.onmousedown = function() { drawing = true; }
-                    canvas.onmouseup = function() { drawing = false; }
+                    document.onmouseup = function() { drawing = false; }
 
                     canvas.onmousemove = function() {
                         if (drawing) {