Index: src/wp-admin/js/nav-menu.js
===================================================================
--- src/wp-admin/js/nav-menu.js	(revision 42022)
+++ src/wp-admin/js/nav-menu.js	(working copy)
@@ -829,6 +829,17 @@
 					}
 				}
 			});
+			$( '#menu-name' ).on('keyup', _.debounce(function (e) {
+				menuName = $( document.getElementById( 'menu-name' ) );
+				menuNameVal = menuName.val();
+				if ( ! menuNameVal || menuNameVal == menuName.attr( 'title' ) || ! menuNameVal.replace( /\s+/, '' ) ) {
+					// Add warning for invalid menu name
+					menuName.parent().addClass( 'form-invalid' );
+				} else {
+					// Remove warning for valid menu name
+					menuName.parent().removeClass( 'form-invalid' );
+				}
+			}, 500));
 			$('#add-custom-links input[type="text"]').keypress(function(e){
 				$('#customlinkdiv').removeClass('form-invalid');
 
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 42022)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -874,7 +874,7 @@
 		) );
 
 		// Navigation Menus
-		$scripts->add( 'nav-menu', "/wp-admin/js/nav-menu$suffix.js", array( 'jquery-ui-sortable', 'jquery-ui-draggable', 'jquery-ui-droppable', 'wp-lists', 'postbox', 'json2' ) );
+		$scripts->add( 'nav-menu', "/wp-admin/js/nav-menu$suffix.js", array( 'jquery-ui-sortable', 'jquery-ui-draggable', 'jquery-ui-droppable', 'wp-lists', 'postbox', 'json2', 'underscore' ) );
 		did_action( 'init' ) && $scripts->localize( 'nav-menu', 'navMenuL10n', array(
 			'noResultsFound' => __( 'No results found.' ),
 			'warnDeleteMenu' => __( "You are about to permanently delete this menu. \n 'Cancel' to stop, 'OK' to delete." ),