diff --git a/core/block_svg.js b/core/block_svg.js
index a4f53ae0b..213f600b0 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -581,7 +581,7 @@ Blockly.BlockSvg.prototype.onMouseDown_ = function(e) {
   }
   // This event has been handled.  No need to bubble up to the document.
   e.stopPropagation();
-  //e.preventDefault();
+  e.preventDefault();
 };
 
 /**
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index 218f7c720..c6e7d3759 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -742,7 +742,7 @@ Blockly.WorkspaceSvg.prototype.onMouseDown_ = function(e) {
   }
   // This event has been handled.  No need to bubble up to the document.
   e.stopPropagation();
-  //e.preventDefault();
+  e.preventDefault();
 };
 
 /**