diff --git a/src/wp-admin/css/admin-menu.css b/src/wp-admin/css/admin-menu.css
index 08638af265..2bb6769de7 100644
--- a/src/wp-admin/css/admin-menu.css
+++ b/src/wp-admin/css/admin-menu.css
@@ -401,7 +401,7 @@ div.wp-menu-image:before {
 /* Sticky admin menu */
 .sticky-menu #adminmenuwrap {
 	position: fixed;
-	z-index: 99; /* Match the z-index of .wp-submenu to ensure flyout menus don't appear underneath main column elements */
+	z-index: 9999; /* Match the z-index of .wp-submenu to ensure flyout menus don't appear underneath main column elements */
 }
 
 /* A new arrow */