diff --git a/wp-includes/class-wp-customize-nav-menus.php b/wp-includes/class-wp-customize-nav-menus.php
index 1044a72e9d..61425d801c 100644
--- a/wp-includes/class-wp-customize-nav-menus.php
+++ b/wp-includes/class-wp-customize-nav-menus.php
@@ -496,6 +496,7 @@ final class WP_Customize_Nav_Menus {
 					'theme_supports'    => 'menus',
 					'type'              => 'theme_mod',
 					'transport'         => 'postMessage',
+					'default'           => 0,
 				) );
 			}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b051a4bc1c..ad3104b9bd 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-beta4-33420';
+$wp_version = '4.3-beta4-33421';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.