diff --git a/core/xml.js b/core/xml.js
index d7461644f..345e23534 100644
--- a/core/xml.js
+++ b/core/xml.js
@@ -193,7 +193,7 @@ Blockly.Xml.blockToDom = function(block, opt_noId) {
       }
       var shadow = input.connection.getShadowDom();
       if (shadow && (!childBlock || !childBlock.isShadow())) {
-        container.appendChild(Blockly.Xml.cloneShadow_(shadow));
+        container.appendChild(Blockly.Xml.cloneShadow_(shadow, opt_noId));
       }
       if (childBlock) {
         container.appendChild(Blockly.Xml.blockToDom(childBlock, opt_noId));
@@ -233,7 +233,7 @@ Blockly.Xml.blockToDom = function(block, opt_noId) {
   }
   var shadow = block.nextConnection && block.nextConnection.getShadowDom();
   if (shadow && (!nextBlock || !nextBlock.isShadow())) {
-    container.appendChild(Blockly.Xml.cloneShadow_(shadow));
+    container.appendChild(Blockly.Xml.cloneShadow_(shadow, opt_noId));
   }
 
   return element;
@@ -242,15 +242,21 @@ Blockly.Xml.blockToDom = function(block, opt_noId) {
 /**
  * Deeply clone the shadow's DOM so that changes don't back-wash to the block.
  * @param {!Element} shadow A tree of XML elements.
+ * @param {boolean=} opt_noId True if the encoder should skip the block ID.
  * @return {!Element} A tree of XML elements.
  * @private
  */
-Blockly.Xml.cloneShadow_ = function(shadow) {
+Blockly.Xml.cloneShadow_ = function(shadow, opt_noId) {
   shadow = shadow.cloneNode(true);
   // Walk the tree looking for whitespace.  Don't prune whitespace in a tag.
   var node = shadow;
   var textNode;
   while (node) {
+    if (opt_noId && node.nodeName == 'shadow') {
+      // Strip off IDs from shadow blocks.  There should never be a 'block' as
+      // a child of a 'shadow', so no need to check that.
+      node.removeAttribute('id');
+    }
     if (node.firstChild) {
       node = node.firstChild;
     } else {