diff --git a/core/components/menu/menu.js b/core/components/menu/menu.js
index 6bad647d7..ab89585db 100644
--- a/core/components/menu/menu.js
+++ b/core/components/menu/menu.js
@@ -44,6 +44,41 @@ Blockly.Menu = function() {
    * @private
    */
   this.highlightedIndex_ = -1;
+
+  /**
+   * Mouse over event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.mouseOverHandler_ = null;
+
+  /**
+   * Click event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.clickHandler_ = null;
+
+  /**
+   * Mouse enter event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.mouseEnterHandler_ = null;
+
+  /**
+   * Mouse leave event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.mouseLeaveHandler_ = null;
+
+  /**
+   * Key down event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onKeyDownWrapper_ = null;
 };
 Blockly.utils.object.inherits(Blockly.Menu, Blockly.Component);
 
@@ -147,7 +182,6 @@ Blockly.Menu.prototype.attachEvents_ = function() {
       'mouseenter', this, this.handleMouseEnter_, true);
   this.mouseLeaveHandler_ = Blockly.bindEventWithChecks_(el,
       'mouseleave', this, this.handleMouseLeave_, true);
-
   this.onKeyDownWrapper_ = Blockly.bindEventWithChecks_(el,
       'keydown', this, this.handleKeyEvent);
 };
@@ -157,11 +191,26 @@ Blockly.Menu.prototype.attachEvents_ = function() {
  * @private
  */
 Blockly.Menu.prototype.detachEvents_ = function() {
-  Blockly.unbindEvent_(this.mouseOverHandler_);
-  Blockly.unbindEvent_(this.clickHandler_);
-  Blockly.unbindEvent_(this.mouseEnterHandler_);
-  Blockly.unbindEvent_(this.mouseLeaveHandler_);
-  Blockly.unbindEvent_(this.onKeyDownWrapper_);
+  if (this.mouseOverHandler_) {
+    Blockly.unbindEvent_(this.mouseOverHandler_);
+    this.mouseOverHandler_ = null;
+  }
+  if (this.clickHandler_) {
+    Blockly.unbindEvent_(this.clickHandler_);
+    this.clickHandler_ = null;
+  }
+  if (this.mouseEnterHandler_) {
+    Blockly.unbindEvent_(this.mouseEnterHandler_);
+    this.mouseEnterHandler_ = null;
+  }
+  if (this.mouseLeaveHandler_) {
+    Blockly.unbindEvent_(this.mouseLeaveHandler_);
+    this.mouseLeaveHandler_ = null;
+  }
+  if (this.onKeyDownWrapper_) {
+    Blockly.unbindEvent_(this.onKeyDownWrapper_);
+    this.onKeyDownWrapper_ = null;
+  }
 };
 
 // Child component management.
diff --git a/core/components/tree/treecontrol.js b/core/components/tree/treecontrol.js
index a498b6938..f42c8089a 100644
--- a/core/components/tree/treecontrol.js
+++ b/core/components/tree/treecontrol.js
@@ -44,6 +44,34 @@ goog.require('Blockly.utils.style');
 Blockly.tree.TreeControl = function(toolbox, config) {
   this.toolbox_ = toolbox;
 
+  /**
+   * Focus event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onFocusWrapper_ = null;
+
+  /**
+   * Blur event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onBlurWrapper_ = null;
+
+  /**
+   * Click event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onClickWrapper_ = null;
+
+  /**
+   * Key down event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onKeydownWrapper_ = null;
+
   Blockly.tree.BaseNode.call(this, '', config);
 
   // The root is open and selected by default.
@@ -272,10 +300,8 @@ Blockly.tree.TreeControl.prototype.attachEvents_ = function() {
       'focus', this, this.handleFocus_);
   this.onBlurWrapper_ = Blockly.bindEvent_(el,
       'blur', this, this.handleBlur_);
-
   this.onClickWrapper_ = Blockly.bindEventWithChecks_(el,
       'click', this, this.handleMouseEvent_);
-
   this.onKeydownWrapper_ = Blockly.bindEvent_(el,
       'keydown', this, this.handleKeyEvent_);
 };
@@ -285,10 +311,22 @@ Blockly.tree.TreeControl.prototype.attachEvents_ = function() {
  * @private
  */
 Blockly.tree.TreeControl.prototype.detachEvents_ = function() {
-  Blockly.unbindEvent_(this.onFocusWrapper_);
-  Blockly.unbindEvent_(this.onBlurWrapper_);
-  Blockly.unbindEvent_(this.onClickWrapper_);
-  Blockly.unbindEvent_(this.onKeydownWrapper_);
+  if (this.onFocusWrapper_) {
+    Blockly.unbindEvent_(this.onFocusWrapper_);
+    this.onFocusWrapper_ = null;
+  }
+  if (this.onBlurWrapper_) {
+    Blockly.unbindEvent_(this.onBlurWrapper_);
+    this.onBlurWrapper_ = null;
+  }
+  if (this.onClickWrapper_) {
+    Blockly.unbindEvent_(this.onClickWrapper_);
+    this.onClickWrapper_ = null;
+  }
+  if (this.onKeydownWrapper_) {
+    Blockly.unbindEvent_(this.onKeydownWrapper_);
+    this.onKeydownWrapper_ = null;
+  }
 };
 
 /**
diff --git a/core/contextmenu.js b/core/contextmenu.js
index 9feee57d8..1c51704f7 100644
--- a/core/contextmenu.js
+++ b/core/contextmenu.js
@@ -166,6 +166,7 @@ Blockly.ContextMenu.hide = function() {
   Blockly.ContextMenu.currentBlock = null;
   if (Blockly.ContextMenu.eventWrapper_) {
     Blockly.unbindEvent_(Blockly.ContextMenu.eventWrapper_);
+    Blockly.ContextMenu.eventWrapper_ = null;
   }
 };
 
diff --git a/core/field_angle.js b/core/field_angle.js
index 3a550bcbb..5b8b75bc3 100644
--- a/core/field_angle.js
+++ b/core/field_angle.js
@@ -330,9 +330,11 @@ Blockly.FieldAngle.prototype.dropdownCreate_ = function() {
   // a click handler on the drag surface to update the value if the surface
   // is clicked.
   this.clickSurfaceWrapper_ =
-      Blockly.bindEventWithChecks_(circle, 'click', this, this.onMouseMove_, true, true);
+      Blockly.bindEventWithChecks_(circle, 'click', this, this.onMouseMove_,
+          true, true);
   this.moveSurfaceWrapper_ =
-      Blockly.bindEventWithChecks_(circle, 'mousemove', this, this.onMouseMove_, true, true);
+      Blockly.bindEventWithChecks_(circle, 'mousemove', this, this.onMouseMove_,
+          true, true);
   return svg;
 };
 
@@ -343,12 +345,15 @@ Blockly.FieldAngle.prototype.dropdownCreate_ = function() {
 Blockly.FieldAngle.prototype.dropdownDispose_ = function() {
   if (this.clickWrapper_) {
     Blockly.unbindEvent_(this.clickWrapper_);
+    this.clickWrapper_ = null;
   }
   if (this.clickSurfaceWrapper_) {
     Blockly.unbindEvent_(this.clickSurfaceWrapper_);
+    this.clickSurfaceWrapper_ = null;
   }
   if (this.moveSurfaceWrapper_) {
     Blockly.unbindEvent_(this.moveSurfaceWrapper_);
+    this.moveSurfaceWrapper_ = null;
   }
   this.gauge_ = null;
   this.line_ = null;
diff --git a/core/field_colour.js b/core/field_colour.js
index 095f29c72..54204553e 100644
--- a/core/field_colour.js
+++ b/core/field_colour.js
@@ -610,18 +610,23 @@ Blockly.FieldColour.prototype.dropdownCreate_ = function() {
 Blockly.FieldColour.prototype.dropdownDispose_ = function() {
   if (this.onClickWrapper_) {
     Blockly.unbindEvent_(this.onClickWrapper_);
+    this.onClickWrapper_ = null;
   }
   if (this.onMouseMoveWrapper_) {
     Blockly.unbindEvent_(this.onMouseMoveWrapper_);
+    this.onMouseMoveWrapper_ = null;
   }
   if (this.onMouseEnterWrapper_) {
     Blockly.unbindEvent_(this.onMouseEnterWrapper_);
+    this.onMouseEnterWrapper_ = null;
   }
   if (this.onMouseLeaveWrapper_) {
     Blockly.unbindEvent_(this.onMouseLeaveWrapper_);
+    this.onMouseLeaveWrapper_ = null;
   }
   if (this.onKeyDownWrapper_) {
     Blockly.unbindEvent_(this.onKeyDownWrapper_);
+    this.onKeyDownWrapper_ = null;
   }
   this.picker_ = null;
   this.highlightedIndex_ = null;
diff --git a/core/field_textinput.js b/core/field_textinput.js
index ff39d69a9..98b12f78d 100644
--- a/core/field_textinput.js
+++ b/core/field_textinput.js
@@ -84,6 +84,13 @@ Blockly.FieldTextInput = function(opt_value, opt_validator, opt_config) {
    * @private
    */
   this.onKeyInputWrapper_ = null;
+
+  /**
+   * Blur input event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onBlurInputWrapper_ = null;
 };
 Blockly.utils.object.inherits(Blockly.FieldTextInput, Blockly.Field);
 
@@ -349,7 +356,6 @@ Blockly.FieldTextInput.prototype.bindInputEvents_ = function(htmlInput) {
   this.onKeyInputWrapper_ =
       Blockly.bindEventWithChecks_(
           htmlInput, 'input', this, this.onHtmlInputChange_);
-
   this.onBlurInputWrapper_ =
       Blockly.bindEventWithChecks_(
           htmlInput, 'blur', this, this.onHtmlInputBlur_);
@@ -362,12 +368,15 @@ Blockly.FieldTextInput.prototype.bindInputEvents_ = function(htmlInput) {
 Blockly.FieldTextInput.prototype.unbindInputEvents_ = function() {
   if (this.onKeyDownWrapper_) {
     Blockly.unbindEvent_(this.onKeyDownWrapper_);
+    this.onKeyDownWrapper_ = null;
   }
   if (this.onKeyInputWrapper_) {
     Blockly.unbindEvent_(this.onKeyInputWrapper_);
+    this.onKeyInputWrapper_ = null;
   }
   if (this.onBlurInputWrapper_) {
     Blockly.unbindEvent_(this.onBlurInputWrapper_);
+    this.onBlurInputWrapper_ = null;
   }
 };
 
diff --git a/core/flyout_button.js b/core/flyout_button.js
index 84898cf37..a8cd5360d 100644
--- a/core/flyout_button.js
+++ b/core/flyout_button.js
@@ -87,6 +87,13 @@ Blockly.FlyoutButton = function(workspace, targetWorkspace, xml, isLabel) {
    * @private
    */
   this.cssClass_ = xml.getAttribute('web-class') || null;
+
+  /**
+   * Mouse up event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onMouseUpWrapper_ = null;
 };
 
 /**
@@ -106,13 +113,6 @@ Blockly.FlyoutButton.prototype.width = 0;
  */
 Blockly.FlyoutButton.prototype.height = 0;
 
-/**
- * Opaque data that can be passed to Blockly.unbindEvent_.
- * @type {Array.<!Array>}
- * @private
- */
-Blockly.FlyoutButton.prototype.onMouseUpWrapper_ = null;
-
 /**
  * Create the button elements.
  * @return {!SVGElement} The button's SVG group.
diff --git a/core/gesture.js b/core/gesture.js
index 536f665fc..6e25b9051 100644
--- a/core/gesture.js
+++ b/core/gesture.js
@@ -162,7 +162,7 @@ Blockly.Gesture = function(e, creatorWorkspace) {
   /**
    * A handle to use to unbind a mouse move listener at the end of a drag.
    * Opaque data returned from Blockly.bindEventWithChecks_.
-   * @type {Array.<!Array>}
+   * @type {?Blockly.EventData}
    * @protected
    */
   this.onMoveWrapper_ = null;
@@ -170,7 +170,7 @@ Blockly.Gesture = function(e, creatorWorkspace) {
   /**
    * A handle to use to unbind a mouse up listener at the end of a drag.
    * Opaque data returned from Blockly.bindEventWithChecks_.
-   * @type {Array.<!Array>}
+   * @type {?Blockly.EventData}
    * @protected
    */
   this.onUpWrapper_ = null;
diff --git a/core/touch_gesture.js b/core/touch_gesture.js
index 8cfa68351..374fdddb5 100644
--- a/core/touch_gesture.js
+++ b/core/touch_gesture.js
@@ -81,7 +81,7 @@ Blockly.TouchGesture = function(e, creatorWorkspace) {
    * A handle to use to unbind the second touch start or pointer down listener
    * at the end of a drag.
    * Opaque data returned from Blockly.bindEventWithChecks_.
-   * @type {Array.<!Array>}
+   * @type {?Blockly.EventData}
    * @private
    */
   this.onStartWrapper_ = null;
diff --git a/core/workspace_comment_svg.js b/core/workspace_comment_svg.js
index 7b9c41268..d8d79ff00 100644
--- a/core/workspace_comment_svg.js
+++ b/core/workspace_comment_svg.js
@@ -49,6 +49,21 @@ goog.require('Blockly.WorkspaceComment');
  */
 Blockly.WorkspaceCommentSvg = function(workspace, content, height, width,
     opt_id) {
+
+  /**
+   * Mouse up event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onMouseUpWrapper_ = null;
+
+  /**
+   * Mouse move event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.onMouseMoveWrapper_ = null;
+
   // Create core elements for the block.
   /**
    * @type {SVGElement}
diff --git a/demos/custom-fields/pitch/field_pitch.js b/demos/custom-fields/pitch/field_pitch.js
index f5bdf505b..3d3621030 100644
--- a/demos/custom-fields/pitch/field_pitch.js
+++ b/demos/custom-fields/pitch/field_pitch.js
@@ -39,6 +39,20 @@ var CustomFields = CustomFields || {};
  */
 CustomFields.FieldPitch = function(text) {
   CustomFields.FieldPitch.superClass_.constructor.call(this, text);
+
+  /**
+   * Click event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.clickWrapper_ = null;
+
+  /**
+   * Move event data.
+   * @type {?Blockly.EventData}
+   * @private
+   */
+  this.moveWrapper_ = null;
 };
 Blockly.utils.object.inherits(CustomFields.FieldPitch, Blockly.FieldTextInput);
 
@@ -112,8 +126,15 @@ CustomFields.FieldPitch.prototype.dropdownCreate_ = function() {
  * @private
  */
 CustomFields.FieldPitch.prototype.dropdownDispose_ = function() {
-  Blockly.unbindEvent_(this.clickWrapper_);
-  Blockly.unbindEvent_(this.moveWrapper_);
+  if (this.clickWrapper_) {
+    Blockly.unbindEvent_(this.clickWrapper_);
+    this.clickWrapper_ = null;
+  }
+  if (this.moveWrapper_) {
+    Blockly.unbindEvent_(this.moveWrapper_);
+    this.moveWrapper_ = null;
+  }
+  this.imageElement_ = null;
 };
 
 /**