diff --git src/wp-admin/js/customize-widgets.js src/wp-admin/js/customize-widgets.js
index ba9e3d1b43..8af1b81506 100644
--- src/wp-admin/js/customize-widgets.js
+++ src/wp-admin/js/customize-widgets.js
@@ -593,7 +593,7 @@
 			var self = this, $widgetInside, $widgetForm, $customizeSidebar,
 				$themeControlsContainer, positionWidget;
 
-			if ( ! this.params.is_wide ) {
+			if ( ! this.params.is_wide || $( window ).width() <= 640 ) {
 				return;
 			}