diff --git a/blockly_uncompressed.js b/blockly_uncompressed.js
index 25c8984d0..bfc627411 100644
--- a/blockly_uncompressed.js
+++ b/blockly_uncompressed.js
@@ -39,13 +39,13 @@ goog.addDependency('../../core/components/tree/treenode.js', ['Blockly.tree.Tree
 goog.addDependency('../../core/connection.js', ['Blockly.Connection'], ['Blockly.Events', 'Blockly.Events.BlockMove', 'Blockly.Xml'], {});
 goog.addDependency('../../core/connection_db.js', ['Blockly.ConnectionDB'], ['Blockly.RenderedConnection'], {});
 goog.addDependency('../../core/constants.js', ['Blockly.constants'], [], {});
-goog.addDependency('../../core/contextmenu.js', ['Blockly.ContextMenu'], ['Blockly.Events', 'Blockly.Events.BlockCreate', 'Blockly.Menu', 'Blockly.MenuItem', 'Blockly.Msg', 'Blockly.Xml', 'Blockly.utils', 'Blockly.utils.Coordinate', 'Blockly.utils.dom', 'Blockly.utils.userAgent'], {});
+goog.addDependency('../../core/contextmenu.js', ['Blockly.ContextMenu'], ['Blockly.Events', 'Blockly.Events.BlockCreate', 'Blockly.Menu', 'Blockly.MenuItem', 'Blockly.Msg', 'Blockly.Xml', 'Blockly.utils', 'Blockly.utils.Coordinate', 'Blockly.utils.Rect', 'Blockly.utils.dom', 'Blockly.utils.userAgent'], {});
 goog.addDependency('../../core/css.js', ['Blockly.Css'], [], {'lang': 'es5'});
 goog.addDependency('../../core/dropdowndiv.js', ['Blockly.DropDownDiv'], ['Blockly.utils.dom', 'Blockly.utils.math', 'Blockly.utils.style'], {});
 goog.addDependency('../../core/events.js', ['Blockly.Events'], ['Blockly.utils'], {});
 goog.addDependency('../../core/events_abstract.js', ['Blockly.Events.Abstract'], ['Blockly.Events'], {});
 goog.addDependency('../../core/extensions.js', ['Blockly.Extensions'], ['Blockly.utils'], {});
-goog.addDependency('../../core/field.js', ['Blockly.Field'], ['Blockly.Events', 'Blockly.Events.BlockChange', 'Blockly.Gesture', 'Blockly.utils', 'Blockly.utils.Size', 'Blockly.utils.dom', 'Blockly.utils.style', 'Blockly.utils.userAgent'], {'lang': 'es5'});
+goog.addDependency('../../core/field.js', ['Blockly.Field'], ['Blockly.Events', 'Blockly.Events.BlockChange', 'Blockly.Gesture', 'Blockly.utils', 'Blockly.utils.Rect', 'Blockly.utils.Size', 'Blockly.utils.dom', 'Blockly.utils.style', 'Blockly.utils.userAgent'], {'lang': 'es5'});
 goog.addDependency('../../core/field_angle.js', ['Blockly.FieldAngle'], ['Blockly.Css', 'Blockly.DropDownDiv', 'Blockly.FieldTextInput', 'Blockly.fieldRegistry', 'Blockly.utils.dom', 'Blockly.utils.math', 'Blockly.utils.object', 'Blockly.utils.userAgent'], {});
 goog.addDependency('../../core/field_checkbox.js', ['Blockly.FieldCheckbox'], ['Blockly.Events', 'Blockly.Events.BlockChange', 'Blockly.Field', 'Blockly.fieldRegistry', 'Blockly.utils.Size', 'Blockly.utils.dom', 'Blockly.utils.object'], {});
 goog.addDependency('../../core/field_colour.js', ['Blockly.FieldColour'], ['Blockly.Css', 'Blockly.DropDownDiv', 'Blockly.Events', 'Blockly.Events.BlockChange', 'Blockly.Field', 'Blockly.fieldRegistry', 'Blockly.navigation', 'Blockly.utils.IdGenerator', 'Blockly.utils.KeyCodes', 'Blockly.utils.Size', 'Blockly.utils.aria', 'Blockly.utils.colour', 'Blockly.utils.dom', 'Blockly.utils.object'], {});
@@ -72,13 +72,13 @@ goog.addDependency('../../core/input.js', ['Blockly.Input'], ['Blockly.Connectio
 goog.addDependency('../../core/insertion_marker_manager.js', ['Blockly.InsertionMarkerManager'], ['Blockly.Events', 'Blockly.blockAnimations'], {'lang': 'es5'});
 goog.addDependency('../../core/interfaces/i_accessibility.js', ['Blockly.IASTNodeLocation', 'Blockly.IASTNodeLocationSvg', 'Blockly.IASTNodeLocationWithBlock', 'Blockly.IBlocklyActionable'], [], {});
 goog.addDependency('../../core/interfaces/i_bounded_element.js', ['Blockly.IBoundedElement'], [], {});
-goog.addDependency('../../core/interfaces/i_copyable.js', ['Blockly.ICopyable'], ['Blockly.ISelectable'], {});
+goog.addDependency('../../core/interfaces/i_copyable.js', ['Blockly.ICopyable'], [], {});
 goog.addDependency('../../core/interfaces/i_deletable.js', ['Blockly.IDeletable'], [], {});
 goog.addDependency('../../core/interfaces/i_deletearea.js', ['Blockly.IDeleteArea'], [], {});
-goog.addDependency('../../core/interfaces/i_disposable.js', ['Blockly.IDisposable'], ['Blockly.Inheritance'], {});
 goog.addDependency('../../core/interfaces/i_movable.js', ['Blockly.IMovable'], [], {});
 goog.addDependency('../../core/interfaces/i_registrable.js', ['Blockly.IRegistrable'], [], {});
-goog.addDependency('../../core/interfaces/i_selectable.js', ['Blockly.ISelectable'], ['Blockly.IDeletable', 'Blockly.IMovable'], {});
+goog.addDependency('../../core/interfaces/i_selectable.js', ['Blockly.ISelectable'], [], {});
+goog.addDependency('../../core/interfaces/i_toolbox.js', ['Blockly.IToolbox'], [], {});
 goog.addDependency('../../core/keyboard_nav/action.js', ['Blockly.Action'], [], {});
 goog.addDependency('../../core/keyboard_nav/ast_node.js', ['Blockly.ASTNode'], ['Blockly.utils.Coordinate'], {'lang': 'es5'});
 goog.addDependency('../../core/keyboard_nav/basic_cursor.js', ['Blockly.BasicCursor'], ['Blockly.ASTNode', 'Blockly.Cursor'], {'lang': 'es5'});
@@ -94,7 +94,7 @@ goog.addDependency('../../core/menuitem.js', ['Blockly.MenuItem'], ['Blockly.uti
 goog.addDependency('../../core/msg.js', ['Blockly.Msg'], ['Blockly.utils.global'], {});
 goog.addDependency('../../core/mutator.js', ['Blockly.Mutator'], ['Blockly.Bubble', 'Blockly.Events', 'Blockly.Events.BlockChange', 'Blockly.Events.Ui', 'Blockly.Icon', 'Blockly.WorkspaceSvg', 'Blockly.Xml', 'Blockly.navigation', 'Blockly.utils', 'Blockly.utils.dom', 'Blockly.utils.global', 'Blockly.utils.object', 'Blockly.utils.xml'], {});
 goog.addDependency('../../core/names.js', ['Blockly.Names'], ['Blockly.Msg'], {});
-goog.addDependency('../../core/options.js', ['Blockly.Options'], ['Blockly.Theme', 'Blockly.Themes.Classic', 'Blockly.Xml', 'Blockly.user.keyMap', 'Blockly.utils.Metrics', 'Blockly.utils.toolbox', 'Blockly.utils.userAgent'], {});
+goog.addDependency('../../core/options.js', ['Blockly.Options'], ['Blockly.Theme', 'Blockly.Themes.Classic', 'Blockly.Xml', 'Blockly.registry', 'Blockly.user.keyMap', 'Blockly.utils.Metrics', 'Blockly.utils.toolbox', 'Blockly.utils.userAgent'], {});
 goog.addDependency('../../core/procedures.js', ['Blockly.Procedures'], ['Blockly.Blocks', 'Blockly.Events', 'Blockly.Events.BlockChange', 'Blockly.Field', 'Blockly.Msg', 'Blockly.Names', 'Blockly.Workspace', 'Blockly.Xml', 'Blockly.constants', 'Blockly.utils.xml'], {});
 goog.addDependency('../../core/registry.js', ['Blockly.registry'], [], {});
 goog.addDependency('../../core/rendered_connection.js', ['Blockly.RenderedConnection'], ['Blockly.Connection', 'Blockly.Events', 'Blockly.utils', 'Blockly.utils.Coordinate', 'Blockly.utils.dom', 'Blockly.utils.object'], {});
@@ -138,7 +138,7 @@ goog.addDependency('../../core/renderers/zelos/path_object.js', ['Blockly.zelos.
 goog.addDependency('../../core/renderers/zelos/renderer.js', ['Blockly.zelos.Renderer'], ['Blockly.InsertionMarkerManager', 'Blockly.blockRendering', 'Blockly.blockRendering.Renderer', 'Blockly.utils.object', 'Blockly.zelos.ConstantProvider', 'Blockly.zelos.Drawer', 'Blockly.zelos.MarkerSvg', 'Blockly.zelos.PathObject', 'Blockly.zelos.RenderInfo'], {});
 goog.addDependency('../../core/requires.js', ['Blockly.requires'], ['Blockly', 'Blockly.Comment', 'Blockly.FieldAngle', 'Blockly.FieldCheckbox', 'Blockly.FieldColour', 'Blockly.FieldDropdown', 'Blockly.FieldImage', 'Blockly.FieldLabelSerializable', 'Blockly.FieldMultilineInput', 'Blockly.FieldNumber', 'Blockly.FieldTextInput', 'Blockly.FieldVariable', 'Blockly.FlyoutButton', 'Blockly.Generator', 'Blockly.HorizontalFlyout', 'Blockly.Mutator', 'Blockly.Themes.Classic', 'Blockly.Themes.Dark', 'Blockly.Themes.Deuteranopia', 'Blockly.Themes.HighContrast', 'Blockly.Themes.Tritanopia', 'Blockly.Toolbox', 'Blockly.Trashcan', 'Blockly.VariablesDynamic', 'Blockly.VerticalFlyout', 'Blockly.Warning', 'Blockly.ZoomControls', 'Blockly.geras.Renderer', 'Blockly.thrasos.Renderer', 'Blockly.zelos.Renderer'], {});
 goog.addDependency('../../core/scrollbar.js', ['Blockly.Scrollbar', 'Blockly.ScrollbarPair'], ['Blockly.Touch', 'Blockly.utils', 'Blockly.utils.Coordinate', 'Blockly.utils.Metrics', 'Blockly.utils.dom'], {});
-goog.addDependency('../../core/theme.js', ['Blockly.Theme'], ['Blockly.utils', 'Blockly.utils.colour', 'Blockly.utils.object'], {});
+goog.addDependency('../../core/theme.js', ['Blockly.Theme'], ['Blockly.registry', 'Blockly.utils', 'Blockly.utils.colour', 'Blockly.utils.object'], {});
 goog.addDependency('../../core/theme/classic.js', ['Blockly.Themes.Classic'], ['Blockly.Theme'], {});
 goog.addDependency('../../core/theme/dark.js', ['Blockly.Themes.Dark'], ['Blockly.Theme'], {});
 goog.addDependency('../../core/theme/deuteranopia.js', ['Blockly.Themes.Deuteranopia'], ['Blockly.Theme'], {});
@@ -147,13 +147,13 @@ goog.addDependency('../../core/theme/modern.js', ['Blockly.Themes.Modern'], ['Bl
 goog.addDependency('../../core/theme/tritanopia.js', ['Blockly.Themes.Tritanopia'], ['Blockly.Theme'], {});
 goog.addDependency('../../core/theme/zelos.js', ['Blockly.Themes.Zelos'], ['Blockly.Theme'], {});
 goog.addDependency('../../core/theme_manager.js', ['Blockly.ThemeManager'], ['Blockly.Theme'], {});
-goog.addDependency('../../core/toolbox.js', ['Blockly.Toolbox'], ['Blockly.Css', 'Blockly.Events', 'Blockly.Events.Ui', 'Blockly.Touch', 'Blockly.navigation', 'Blockly.tree.TreeControl', 'Blockly.tree.TreeNode', 'Blockly.utils', 'Blockly.utils.Rect', 'Blockly.utils.aria', 'Blockly.utils.colour', 'Blockly.utils.dom', 'Blockly.utils.object', 'Blockly.utils.toolbox'], {});
+goog.addDependency('../../core/toolbox.js', ['Blockly.Toolbox'], ['Blockly.Css', 'Blockly.Events', 'Blockly.Events.Ui', 'Blockly.Touch', 'Blockly.navigation', 'Blockly.registry', 'Blockly.tree.TreeControl', 'Blockly.tree.TreeNode', 'Blockly.utils', 'Blockly.utils.Rect', 'Blockly.utils.aria', 'Blockly.utils.colour', 'Blockly.utils.dom', 'Blockly.utils.object', 'Blockly.utils.toolbox'], {});
 goog.addDependency('../../core/tooltip.js', ['Blockly.Tooltip'], ['Blockly.utils.string'], {});
 goog.addDependency('../../core/touch.js', ['Blockly.Touch'], ['Blockly.utils', 'Blockly.utils.global', 'Blockly.utils.string'], {});
 goog.addDependency('../../core/touch_gesture.js', ['Blockly.TouchGesture'], ['Blockly.Gesture', 'Blockly.utils', 'Blockly.utils.Coordinate', 'Blockly.utils.object'], {});
 goog.addDependency('../../core/trashcan.js', ['Blockly.Trashcan'], ['Blockly.Scrollbar', 'Blockly.Xml', 'Blockly.utils.Rect', 'Blockly.utils.dom'], {});
 goog.addDependency('../../core/ui_events.js', ['Blockly.Events.Ui'], ['Blockly.Events', 'Blockly.Events.Abstract', 'Blockly.utils.object'], {});
-goog.addDependency('../../core/utils.js', ['Blockly.utils'], ['Blockly.Msg', 'Blockly.constants', 'Blockly.utils.Coordinate', 'Blockly.utils.colour', 'Blockly.utils.global', 'Blockly.utils.string', 'Blockly.utils.style', 'Blockly.utils.userAgent'], {});
+goog.addDependency('../../core/utils.js', ['Blockly.utils'], ['Blockly.Msg', 'Blockly.constants', 'Blockly.utils.Coordinate', 'Blockly.utils.Rect', 'Blockly.utils.colour', 'Blockly.utils.global', 'Blockly.utils.string', 'Blockly.utils.style', 'Blockly.utils.userAgent'], {});
 goog.addDependency('../../core/utils/aria.js', ['Blockly.utils.aria'], [], {});
 goog.addDependency('../../core/utils/colour.js', ['Blockly.utils.colour'], [], {});
 goog.addDependency('../../core/utils/coordinate.js', ['Blockly.utils.Coordinate'], [], {});
@@ -187,7 +187,7 @@ goog.addDependency('../../core/workspace_comment_svg.js', ['Blockly.WorkspaceCom
 goog.addDependency('../../core/workspace_drag_surface_svg.js', ['Blockly.WorkspaceDragSurfaceSvg'], ['Blockly.utils', 'Blockly.utils.dom'], {});
 goog.addDependency('../../core/workspace_dragger.js', ['Blockly.WorkspaceDragger'], ['Blockly.utils.Coordinate'], {});
 goog.addDependency('../../core/workspace_events.js', ['Blockly.Events.FinishedLoading'], ['Blockly.Events', 'Blockly.Events.Ui', 'Blockly.utils.object'], {'lang': 'es5'});
-goog.addDependency('../../core/workspace_svg.js', ['Blockly.WorkspaceSvg'], ['Blockly.BlockSvg', 'Blockly.ConnectionDB', 'Blockly.Events', 'Blockly.Events.BlockCreate', 'Blockly.Gesture', 'Blockly.Grid', 'Blockly.MarkerManager', 'Blockly.Msg', 'Blockly.Options', 'Blockly.ThemeManager', 'Blockly.Themes.Classic', 'Blockly.TouchGesture', 'Blockly.Workspace', 'Blockly.WorkspaceAudio', 'Blockly.WorkspaceDragSurfaceSvg', 'Blockly.Xml', 'Blockly.blockRendering', 'Blockly.constants', 'Blockly.navigation', 'Blockly.utils', 'Blockly.utils.Coordinate', 'Blockly.utils.Metrics', 'Blockly.utils.Rect', 'Blockly.utils.dom', 'Blockly.utils.object', 'Blockly.utils.toolbox'], {});
+goog.addDependency('../../core/workspace_svg.js', ['Blockly.WorkspaceSvg'], ['Blockly.BlockSvg', 'Blockly.ConnectionDB', 'Blockly.Events', 'Blockly.Events.BlockCreate', 'Blockly.Gesture', 'Blockly.Grid', 'Blockly.MarkerManager', 'Blockly.Msg', 'Blockly.Options', 'Blockly.ThemeManager', 'Blockly.Themes.Classic', 'Blockly.TouchGesture', 'Blockly.Workspace', 'Blockly.WorkspaceAudio', 'Blockly.WorkspaceDragSurfaceSvg', 'Blockly.Xml', 'Blockly.blockRendering', 'Blockly.constants', 'Blockly.navigation', 'Blockly.registry', 'Blockly.utils', 'Blockly.utils.Coordinate', 'Blockly.utils.Metrics', 'Blockly.utils.Rect', 'Blockly.utils.dom', 'Blockly.utils.object', 'Blockly.utils.toolbox'], {});
 goog.addDependency('../../core/ws_comment_events.js', ['Blockly.Events.CommentBase', 'Blockly.Events.CommentChange', 'Blockly.Events.CommentCreate', 'Blockly.Events.CommentDelete', 'Blockly.Events.CommentMove'], ['Blockly.Events', 'Blockly.Events.Abstract', 'Blockly.utils.Coordinate', 'Blockly.utils.object', 'Blockly.utils.xml'], {});
 goog.addDependency('../../core/xml.js', ['Blockly.Xml'], ['Blockly.Events', 'Blockly.Events.BlockCreate', 'Blockly.Events.FinishedLoading', 'Blockly.Events.VarCreate', 'Blockly.utils', 'Blockly.utils.dom', 'Blockly.utils.global', 'Blockly.utils.xml'], {});
 goog.addDependency('../../core/zoom_controls.js', ['Blockly.ZoomControls'], ['Blockly.Css', 'Blockly.Scrollbar', 'Blockly.Touch', 'Blockly.utils.dom'], {'lang': 'es5'});
diff --git a/core/options.js b/core/options.js
index a9e76ff8c..75151b104 100644
--- a/core/options.js
+++ b/core/options.js
@@ -14,7 +14,9 @@ goog.provide('Blockly.Options');
 
 goog.require('Blockly.Theme');
 goog.require('Blockly.Themes.Classic');
+goog.require('Blockly.registry');
 goog.require('Blockly.user.keyMap');
+goog.require('Blockly.utils.IdGenerator');
 goog.require('Blockly.utils.Metrics');
 goog.require('Blockly.utils.toolbox');
 goog.require('Blockly.utils.userAgent');
@@ -316,10 +318,14 @@ Blockly.Options.parseGridOptions_ = function(options) {
  */
 Blockly.Options.parseThemeOptions_ = function(options) {
   var theme = options['theme'] || Blockly.Themes.Classic;
-  if (theme instanceof Blockly.Theme) {
+  if (typeof theme == 'string') {
+    return /** @type {!Blockly.Theme} */ (
+      Blockly.registry.getObject(Blockly.registry.Type.THEME, theme));
+  } else if (theme instanceof Blockly.Theme) {
     return /** @type {!Blockly.Theme} */ (theme);
   }
-  return Blockly.Theme.defineTheme('builtin', theme);
+  return Blockly.Theme.defineTheme(
+      'builtin' + Blockly.utils.IdGenerator.getNextUniqueId(), theme);
 };
 
 /**
diff --git a/core/registry.js b/core/registry.js
index a9d258ffc..ec7224c2c 100644
--- a/core/registry.js
+++ b/core/registry.js
@@ -16,6 +16,7 @@ goog.provide('Blockly.registry');
 goog.requireType('Blockly.blockRendering.Renderer');
 goog.requireType('Blockly.Field');
 goog.requireType('Blockly.IToolbox');
+goog.requireType('Blockly.Theme');
 goog.requireType('Blockly.utils.toolbox');
 
 
@@ -63,6 +64,9 @@ Blockly.registry.Type.FIELD = new Blockly.registry.Type('field');
 /** @type {!Blockly.registry.Type<Blockly.IToolbox>} */
 Blockly.registry.Type.TOOLBOX = new Blockly.registry.Type('toolbox');
 
+/** @type {!Blockly.registry.Type<Blockly.Theme>} */
+Blockly.registry.Type.THEME = new Blockly.registry.Type('theme');
+
 /**
  * Registers a class based on a type and name.
  * @param {string|Blockly.registry.Type<T>} type The type of the plugin.
diff --git a/core/renderers/common/block_rendering.js b/core/renderers/common/block_rendering.js
index 83cbf9d72..8b4a2b572 100644
--- a/core/renderers/common/block_rendering.js
+++ b/core/renderers/common/block_rendering.js
@@ -20,13 +20,6 @@ goog.require('Blockly.registry');
 goog.require('Blockly.utils.object');
 
 
-/**
- * The set of all registered renderers, keyed by their name.
- * @type {!Object<string, !Function>}
- * @private
- */
-Blockly.blockRendering.rendererMap_ = {};
-
 /**
  * Whether or not the debugger is turned on.
  * @type {boolean}
diff --git a/core/theme.js b/core/theme.js
index e314b7642..f66021f4d 100644
--- a/core/theme.js
+++ b/core/theme.js
@@ -11,6 +11,7 @@
 
 goog.provide('Blockly.Theme');
 
+goog.require('Blockly.registry');
 goog.require('Blockly.utils');
 goog.require('Blockly.utils.colour');
 goog.require('Blockly.utils.object');
@@ -73,6 +74,9 @@ Blockly.Theme = function(name, opt_blockStyles, opt_categoryStyles,
    * @package
    */
   this.startHats = null;
+
+  // Register the theme by name.
+  Blockly.registry.register(Blockly.registry.Type.THEME, name, this);
 };
 
 /**
@@ -206,9 +210,14 @@ Blockly.Theme.prototype.setStartHats = function(startHats) {
 Blockly.Theme.defineTheme = function(name, themeObj) {
   var theme = new Blockly.Theme(name);
   var base = themeObj['base'];
-  if (base && base instanceof Blockly.Theme) {
-    Blockly.utils.object.deepMerge(theme, base);
-    theme.name = name;
+  if (base) {
+    if (typeof base == "string") {
+      base = Blockly.registry.getObject(Blockly.registry.Type.THEME, base);
+    }
+    if (base instanceof Blockly.Theme) {
+      Blockly.utils.object.deepMerge(theme, base);
+      theme.name = name;
+    }
   }
 
   Blockly.utils.object.deepMerge(theme.blockStyles,
@@ -222,5 +231,6 @@ Blockly.Theme.defineTheme = function(name, themeObj) {
   if (themeObj['startHats'] != null) {
     theme.startHats = themeObj['startHats'];
   }
+
   return theme;
 };
diff --git a/core/utils/idgenerator.js b/core/utils/idgenerator.js
index 81bd405a6..e17c51f31 100644
--- a/core/utils/idgenerator.js
+++ b/core/utils/idgenerator.js
@@ -29,5 +29,5 @@ Blockly.utils.IdGenerator.nextId_ = 0;
  * @return {string} The next unique identifier.
  */
 Blockly.utils.IdGenerator.getNextUniqueId = function() {
-  return 'blockly:' + (Blockly.utils.IdGenerator.nextId_++).toString(36);
+  return 'blockly-' + (Blockly.utils.IdGenerator.nextId_++).toString(36);
 };
diff --git a/tests/mocha/block_test.js b/tests/mocha/block_test.js
index 08f11a84b..3375c57bb 100644
--- a/tests/mocha/block_test.js
+++ b/tests/mocha/block_test.js
@@ -1657,6 +1657,8 @@ suite('Blocks', function() {
       });
       teardown(function() {
         this.workspace.dispose();
+        // Clear all registered themes.
+        Blockly.registry.typeMap_['theme'] = {};
       });
       test('Set colour hue', function() {
         this.block.setColour('20');
diff --git a/tests/mocha/theme_test.js b/tests/mocha/theme_test.js
index d9c15d709..3e7c18a8f 100644
--- a/tests/mocha/theme_test.js
+++ b/tests/mocha/theme_test.js
@@ -11,6 +11,10 @@
 'use strict';
 
 suite('Theme', function() {
+  teardown(function() {
+    // Clear all registered themes.
+    Blockly.registry.typeMap_['theme'] = {};
+  });
 
   function defineThemeTestBlocks() {
     Blockly.defineBlocksWithJsonArray([{