diff --git a/wp-admin/admin-header.php b/wp-admin/admin-header.php
index 6aba1c14d5..c7a0066a3f 100644
--- a/wp-admin/admin-header.php
+++ b/wp-admin/admin-header.php
@@ -99,7 +99,12 @@ $admin_body_class .= ' no-customize-support';
 	document.body.className = document.body.className.replace('no-js','js');
 </script>
 
-<?php wp_customize_support_script(); ?>
+<?php
+// If the customize-loader script is enqueued, make sure the customize
+// body classes are correct as early as possible.
+if ( wp_script_is( 'customize-loader', 'queue' ) )
+	wp_customize_support_script();
+?>
 
 <div id="wpwrap">
 <?php require(ABSPATH . 'wp-admin/menu-header.php'); ?>
diff --git a/wp-includes/admin-bar.php b/wp-includes/admin-bar.php
index 8e90085d00..6a5489cc47 100644
--- a/wp-includes/admin-bar.php
+++ b/wp-includes/admin-bar.php
@@ -576,7 +576,16 @@ function wp_admin_bar_appearance_menu( $wp_admin_bar ) {
 	if ( ! current_user_can( 'edit_theme_options' ) )
 		return;
 
-	$wp_admin_bar->add_menu( array( 'parent' => 'appearance', 'id' => 'customize', 'title' => __('Customize'), 'href' => wp_customize_url(get_stylesheet()) ) );
+	$wp_admin_bar->add_menu( array(
+		'parent' => 'appearance',
+		'id'     => 'customize',
+		'title'  => __('Customize'),
+		'href'   => wp_customize_url(get_stylesheet()),
+		'meta'   => array(
+			'class' => 'hide-if-no-customize',
+		),
+	) );
+	add_action( 'wp_before_admin_bar_render', 'wp_customize_support_script' );
 
 	if ( current_theme_supports( 'widgets' )  )
 		$wp_admin_bar->add_menu( array( 'parent' => 'appearance', 'id' => 'widgets', 'title' => __('Widgets'), 'href' => admin_url('widgets.php') ) );
diff --git a/wp-includes/css/admin-bar.dev.css b/wp-includes/css/admin-bar.dev.css
index 5cf65c2fd1..d4e2309a88 100644
--- a/wp-includes/css/admin-bar.dev.css
+++ b/wp-includes/css/admin-bar.dev.css
@@ -581,6 +581,14 @@
 	background-position: -2px -203px;
 }
 
+/**
+ * Customize support classes
+ */
+.no-customize-support .hide-if-no-customize,
+.customize-support .hide-if-customize {
+	display: none;
+}
+
 /**
  * Retina display 2x icons
  */
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index eae3f4e207..5485b3ed52 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -1636,9 +1636,6 @@ function wp_customize_url( $stylesheet ) {
  * @since 3.4.0
  */
 function wp_customize_support_script() {
-	if ( ! wp_script_is( 'customize-loader', 'queue' ) )
-		return;
-
 	$admin_origin = parse_url( admin_url() );
 	$home_origin  = parse_url( home_url() );
 	$cross_domain = ( strtolower( $admin_origin[ 'host' ] ) != strtolower( $home_origin[ 'host' ] ) );