diff --git a/core/block.js b/core/block.js
index 6eb1f3628..9a5b32200 100644
--- a/core/block.js
+++ b/core/block.js
@@ -322,6 +322,8 @@ Blockly.Block.prototype.dispose = function(healStack) {
   } finally {
     Blockly.Events.enable();
   }
+
+  this.disposed = true;
 };
 
 /**