diff --git a/package.json b/package.json
index 61dca06b40..f409f0d9db 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
   "author": "The WordPress Contributors",
   "license": "GPL-2.0+",
   "devDependencies": {
-    "autoprefixer": "~6.3.3",
+    "autoprefixer": "^6.5.0",
     "grunt": "~0.4.5",
     "grunt-browserify": "~5.0.0",
     "grunt-contrib-clean": "~1.0.0",
diff --git a/src/wp-admin/css/customize-nav-menus.css b/src/wp-admin/css/customize-nav-menus.css
index d180fb3b35..eddc6c19de 100644
--- a/src/wp-admin/css/customize-nav-menus.css
+++ b/src/wp-admin/css/customize-nav-menus.css
@@ -568,6 +568,7 @@
 }
 
 #available-menu-items .accordion-section-content .new-content-item {
+	width: -webkit-calc(100% - 30px);
 	width: calc(100% - 30px);
 	padding: 8px 15px;
 	position: absolute;