diff --git a/src/wp-includes/customize/class-wp-customize-nav-menu-section.php b/src/wp-includes/customize/class-wp-customize-nav-menu-section.php
index fb5eb76891..5518b34705 100644
--- a/src/wp-includes/customize/class-wp-customize-nav-menu-section.php
+++ b/src/wp-includes/customize/class-wp-customize-nav-menu-section.php
@@ -36,7 +36,7 @@ class WP_Customize_Nav_Menu_Section extends WP_Customize_Section {
 	 */
 	public function json() {
 		$exported = parent::json();
-		$exported['menu_id'] = intval( preg_replace( '/^nav_menu\[(\d+)\]/', '$1', $this->id ) );
+		$exported['menu_id'] = intval( preg_replace( '/^nav_menu\[(-?\d+)\]/', '$1', $this->id ) );
 
 		return $exported;
 	}