diff --git a/src/wp-admin/customize.php b/src/wp-admin/customize.php
index 3cfa0c7..33c167c 100644
--- a/src/wp-admin/customize.php
+++ b/src/wp-admin/customize.php
@@ -228,6 +228,7 @@ do_action( 'customize_controls_print_scripts' );
 
 	// Prepare customizer settings to pass to Javascript.
 	$settings = array(
+		'isDefaultCustomizerInstance' => true,
 		'theme'    => array(
 			'stylesheet' => $wp_customize->get_stylesheet(),
 			'active'     => $wp_customize->is_theme_active(),
diff --git a/src/wp-admin/js/customize-controls.js b/src/wp-admin/js/customize-controls.js
index 85b171d..919309b 100644
--- a/src/wp-admin/js/customize-controls.js
+++ b/src/wp-admin/js/customize-controls.js
@@ -980,7 +980,10 @@
 		header: api.HeaderControl
 	};
 
-	$( function() {
+	/**
+	 * Bootstraps the default customizer instance (on customize.php).
+	 */
+	var bootstrapDefaultCustomizerInstance = function() {
 		api.settings = window._wpCustomizeSettings;
 		api.l10n = window._wpCustomizeControlsL10n;
 
@@ -988,6 +991,9 @@
 		if ( ! api.settings )
 			return;
 
+		if ( ! api.settings.isDefaultCustomizerInstance )
+			return;
+
 		// Redirect to the fallback preview if any incompatibilities are found.
 		if ( ! $.support.postMessage || ( ! $.support.cors && api.settings.isCrossDomain ) )
 			return window.location = api.settings.url.fallback;
@@ -1299,7 +1305,8 @@
 		setTimeout(function () {
 			topFocus.focus();
 		}, 200);
+	};
 
-	});
+	$( bootstrapDefaultCustomizerInstance );
 
-})( wp, jQuery );
+})( wp, jQuery );
\ No newline at end of file