diff --git a/core/events.js b/core/events.js
index 2d0ae0b1b..2a00f205a 100644
--- a/core/events.js
+++ b/core/events.js
@@ -95,7 +95,7 @@ Blockly.Events.fireNow_ = function() {
   for (var i = 0, detail; detail = queue[i]; i++) {
     console.log(detail);
     var workspace = Blockly.Workspace.getById(detail.workspaceId);
-    if (workspace.rendered) {
+    if (workspace && workspace.rendered) {
       // Create a custom event in a browser-compatible way.
       if (typeof CustomEvent == 'function') {
         // W3
@@ -124,11 +124,21 @@ Blockly.Events.filter_ = function(queueIn) {
       if (event1.type == Blockly.Events.MOVE &&
           event2.type == Blockly.Events.MOVE &&
           event1.blockId == event2.blockId) {
+        // Merge move events.
         event1.newParentId = event2.newParentId;
         event1.newInputName = event2.newInputName;
         event1.newCoordinate = event2.newCoordinate;
         queue.splice(j, 1);
         j--;
+      } else if (event1.type == Blockly.Events.CHANGE &&
+          event2.type == Blockly.Events.CHANGE &&
+          event1.blockId == event2.blockId &&
+          event1.element == event2.element &&
+          event1.name == event2.name) {
+        // Merge change events.
+        event1.newValue = event2.newValue;
+        queue.splice(j, 1);
+        j--;
       }
     }
   }
diff --git a/core/mutator.js b/core/mutator.js
index 430b58af0..5f51f97bf 100644
--- a/core/mutator.js
+++ b/core/mutator.js
@@ -283,6 +283,7 @@ Blockly.Mutator.prototype.workspaceChanged_ = function() {
 
   // When the mutator's workspace changes, update the source block.
   if (this.rootBlock_.workspace == this.workspace_) {
+    var oldMutation = this.block_.mutationToDom();
     // Switch off rendering while the source block is rebuilt.
     var savedRendered = this.block_.rendered;
     this.block_.rendered = false;
@@ -292,12 +293,18 @@ Blockly.Mutator.prototype.workspaceChanged_ = function() {
     this.block_.rendered = savedRendered;
     // Mutation may have added some elements that need initalizing.
     this.block_.initSvg();
+    var newMutation = this.block_.mutationToDom();
+    if (Blockly.Xml.domToText(oldMutation) !=
+        Blockly.Xml.domToText(newMutation)) {
+      Blockly.Events.fire(new Blockly.Events.Change(
+          this.block_, 'mutation', null, oldMutation, newMutation));
+      goog.Timer.callOnce(
+          this.block_.bumpNeighbours_, Blockly.BUMP_DELAY, this.block_);
+    }
     if (this.block_.rendered) {
       this.block_.render();
     }
     this.resizeBubble_();
-    goog.Timer.callOnce(
-        this.block_.bumpNeighbours_, Blockly.BUMP_DELAY, this.block_);
   }
 };