diff --git a/wp-includes/widgets/class-wp-nav-menu-widget.php b/wp-includes/widgets/class-wp-nav-menu-widget.php
index 9c3e8d2..b41e9aa 100644
--- a/wp-includes/widgets/class-wp-nav-menu-widget.php
+++ b/wp-includes/widgets/class-wp-nav-menu-widget.php
@@ -153,6 +153,22 @@ class WP_Nav_Menu_Widget extends WP_Widget {
 
 		$nav_menu = ! empty( $instance['nav_menu'] ) ? wp_get_nav_menu_object( $instance['nav_menu'] ) : false;
 
+		// Show notice if no menu is selected or menu is empty (admins only).
+		if ( ! $nav_menu || ! wp_get_nav_menu_items( $nav_menu->term_id ) ) {
+			if ( current_user_can( 'edit_theme_options' ) ) {
+				echo $args['before_widget'];
+
+				if ( ! empty( $instance['title'] ) ) {
+					echo $args['before_title'] . apply_filters( 'widget_title', $instance['title'] ) . $args['after_title'];
+				}
+
+				echo '<p class="nav-menu-widget-notice">' .
+					esc_html__( 'Please select a menu or add items to the selected menu.', 'default' ) .
+					'</p>';
+
+				echo $args['after_widget'];
+			}
+			return;
+		}
+
 		/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
 		$title = apply_filters( 'widget_title', $instance['title'], $instance, $this->id_base );