diff --git a/core/block_svg.js b/core/block_svg.js
index 29d6d8db5..b3ebab4fc 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -927,11 +927,15 @@ Blockly.BlockSvg.prototype.dispose = function(healStack, animate) {
 
 /**
  * Encode a block for copying.
- * @return {!Blockly.ICopyable.CopyData} Copy metadata.
+ * @return {?Blockly.ICopyable.CopyData} Copy metadata, or null if the block is
+ *     an insertion marker.
  * @package
  */
 Blockly.BlockSvg.prototype.toCopyData = function() {
-  var xml = Blockly.Xml.blockToDom(this, true);
+  if (this.isInsertionMarker_) {
+    return null;
+  }
+  var xml = /** @type {!Element} */ (Blockly.Xml.blockToDom(this, true));
   // Copy only the selected block and internal blocks.
   Blockly.Xml.deleteNext(xml);
   // Encode start position in XML.
diff --git a/core/blockly.js b/core/blockly.js
index 997ce3710..1c7025c30 100644
--- a/core/blockly.js
+++ b/core/blockly.js
@@ -272,9 +272,11 @@ Blockly.onKeyDown = function(e) {
  */
 Blockly.copy_ = function(toCopy) {
   var data = toCopy.toCopyData();
-  Blockly.clipboardXml_ = data.xml;
-  Blockly.clipboardSource_ = data.source;
-  Blockly.clipboardTypeCounts_ = data.typeCounts;
+  if (data) {
+    Blockly.clipboardXml_ = data.xml;
+    Blockly.clipboardSource_ = data.source;
+    Blockly.clipboardTypeCounts_ = data.typeCounts;
+  }
 };
 
 /**
diff --git a/core/connection.js b/core/connection.js
index 556fb69f9..6077d0cb2 100644
--- a/core/connection.js
+++ b/core/connection.js
@@ -115,7 +115,8 @@ Blockly.Connection.prototype.connect_ = function(childConnection) {
     // Displaced shadow blocks dissolve rather than reattaching or bumping.
     if (orphanBlock.isShadow()) {
       // Save the shadow block so that field values are preserved.
-      shadowDom = Blockly.Xml.blockToDom(orphanBlock);
+      // This cast assumes that a block can not be both a shadow block and an insertion marker.
+      shadowDom = /** @type {!Element} */ (Blockly.Xml.blockToDom(orphanBlock));
       orphanBlock.dispose(false);
       orphanBlock = null;
     } else if (parentConnection.type == Blockly.INPUT_VALUE) {
diff --git a/core/flyout_base.js b/core/flyout_base.js
index 1a3c6f966..25333d41f 100644
--- a/core/flyout_base.js
+++ b/core/flyout_base.js
@@ -948,7 +948,8 @@ Blockly.Flyout.prototype.placeNewBlock_ = function(oldBlock) {
   }
 
   // Create the new block by cloning the block in the flyout (via XML).
-  var xml = Blockly.Xml.blockToDom(oldBlock, true);
+  // This cast assumes that the oldBlock can not be an insertion marker.
+  var xml = /** @type {!Element} */ (Blockly.Xml.blockToDom(oldBlock, true));
   // The target workspace would normally resize during domToBlock, which will
   // lead to weird jumps.  Save it for terminateDrag.
   targetWorkspace.setResizesEnabled(false);
diff --git a/core/interfaces/i_copyable.js b/core/interfaces/i_copyable.js
index a20565dc5..4aeac9776 100644
--- a/core/interfaces/i_copyable.js
+++ b/core/interfaces/i_copyable.js
@@ -25,7 +25,7 @@ Blockly.ICopyable = function() {};
 
 /**
  * Encode for copying.
- * @return {!Blockly.ICopyable.CopyData} Copy metadata.
+ * @return {?Blockly.ICopyable.CopyData} Copy metadata.
  */
 Blockly.ICopyable.prototype.toCopyData;
 
diff --git a/core/trashcan.js b/core/trashcan.js
index 9502a1445..7820512c8 100644
--- a/core/trashcan.js
+++ b/core/trashcan.js
@@ -606,7 +606,8 @@ Blockly.Trashcan.prototype.onDelete_ = function(event) {
   if (this.workspace_.options.maxTrashcanContents <= 0) {
     return;
   }
-  if (event.type == Blockly.Events.BLOCK_DELETE &&
+  // Must check that the tagName exists since oldXml can be a DocumentFragment.
+  if (event.type == Blockly.Events.BLOCK_DELETE && event.oldXml.tagName &&
       event.oldXml.tagName.toLowerCase() != 'shadow') {
     var cleanedXML = this.cleanBlockXML_(event.oldXml);
     if (this.contents_.indexOf(cleanedXML) != -1) {
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index 84d697b00..feba580ae 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -1326,13 +1326,16 @@ Blockly.WorkspaceSvg.prototype.highlightBlock = function(id, opt_state) {
 
 /**
  * Paste the provided block onto the workspace.
- * @param {!Element} xmlBlock XML block element.
+ * @param {!Element|!DocumentFragment} xmlBlock XML block element or an empty
+ *     DocumentFragment if the block was an insertion marker.
  */
 Blockly.WorkspaceSvg.prototype.paste = function(xmlBlock) {
-  if (!this.rendered || xmlBlock.getElementsByTagName('block').length >=
+  if (!this.rendered || !xmlBlock.tagName || xmlBlock.getElementsByTagName('block').length >=
       this.remainingCapacity()) {
     return;
   }
+  // The check above for tagName rules out the possibility of this being a DocumentFragment.
+  xmlBlock = /** @type {!Element} */ (xmlBlock);
   if (this.currentGesture_) {
     this.currentGesture_.cancel();  // Dragging while pasting?  No.
   }
diff --git a/core/xml.js b/core/xml.js
index ae245b864..20c82015b 100644
--- a/core/xml.js
+++ b/core/xml.js
@@ -74,15 +74,15 @@ Blockly.Xml.variablesToDom = function(variableList) {
  * Encode a block subtree as XML with XY coordinates.
  * @param {!Blockly.Block} block The root block to encode.
  * @param {boolean=} opt_noId True if the encoder should skip the block ID.
- * @return {!Element} Tree of XML elements.
+ * @return {!Element|!DocumentFragment} Tree of XML elements or an empty document
+ *     fragment if the block was an insertion marker.
  */
 Blockly.Xml.blockToDomWithXY = function(block, opt_noId) {
   if (block.isInsertionMarker()) {  // Skip over insertion markers.
     block = block.getChildren(false)[0];
     if (!block) {
-      // Disappears when appended. Cast to ANY b/c DocumentFragment -> Element
-      // is invalid. We have to cast to ANY in between.
-      return /** @type{?} */ (new DocumentFragment());
+      // Disappears when appended.
+      return new DocumentFragment();
     }
   }
 
@@ -138,7 +138,8 @@ Blockly.Xml.allFieldsToDom_ = function(block, element) {
  * Encode a block subtree as XML.
  * @param {!Blockly.Block} block The root block to encode.
  * @param {boolean=} opt_noId True if the encoder should skip the block ID.
- * @return {!Element} Tree of XML elements.
+ * @return {!Element|!DocumentFragment} Tree of XML elements or an empty document
+ *     fragment if the block was an insertion marker.
  */
 Blockly.Xml.blockToDom = function(block, opt_noId) {
   // Skip over insertion markers.
@@ -147,9 +148,8 @@ Blockly.Xml.blockToDom = function(block, opt_noId) {
     if (child) {
       return Blockly.Xml.blockToDom(child);
     } else {
-      // Disappears when appended. Cast to ANY b/c DocumentFragment -> Element
-      // is invalid. We have to cast to ANY in between.
-      return /** @type{?} */ (new DocumentFragment());
+      // Disappears when appended.
+      return new DocumentFragment();
     }
   }
 
@@ -808,7 +808,8 @@ Blockly.Xml.domToField_ = function(block, fieldName, xml) {
 
 /**
  * Remove any 'next' block (statements in a stack).
- * @param {!Element} xmlBlock XML block element.
+ * @param {!Element|!DocumentFragment} xmlBlock XML block element or an empty
+ *     DocumentFragment if the block was an insertion marker.
  */
 Blockly.Xml.deleteNext = function(xmlBlock) {
   for (var i = 0, child; (child = xmlBlock.childNodes[i]); i++) {