diff --git a/core/events.js b/core/events.js
index 8e90f6583..7570fb8e9 100644
--- a/core/events.js
+++ b/core/events.js
@@ -651,8 +651,8 @@ Blockly.Events.Ui.prototype.type = Blockly.Events.UI;
  * Encode the event as JSON.
  * @return {!Object} JSON representation.
  */
-Blockly.Events.Change.prototype.toJson = function() {
-  var json = Blockly.Events.Change.superClass_.toJson.call(this);
+Blockly.Events.Ui.prototype.toJson = function() {
+  var json = Blockly.Events.Ui.superClass_.toJson.call(this);
   json['element'] = this.element;
   if (this.newValue !== undefined) {
     json['newValue'] = this.newValue;
diff --git a/core/toolbox.js b/core/toolbox.js
index c8818be1c..3951c107d 100644
--- a/core/toolbox.js
+++ b/core/toolbox.js
@@ -404,6 +404,7 @@ Blockly.Toolbox.TreeControl.prototype.setSelectedItem = function(node) {
     // not rendered.
     toolbox.addColour_(node);
   }
+  var oldNode = this.getSelectedItem();
   goog.ui.tree.TreeControl.prototype.setSelectedItem.call(this, node);
   if (node && node.blocks && node.blocks.length) {
     toolbox.flyout_.show(node.blocks);
@@ -415,6 +416,12 @@ Blockly.Toolbox.TreeControl.prototype.setSelectedItem = function(node) {
     // Hide the flyout.
     toolbox.flyout_.hide();
   }
+  if (oldNode != node && oldNode != this) {
+    var event = new Blockly.Events.Ui(null, 'category',
+        oldNode && oldNode.getHtml(), node && node.getHtml());
+    event.workspaceId = toolbox.workspace_.id;
+    Blockly.Events.fire(event);
+  }
   if (node) {
     toolbox.lastCategory_ = node;
   }