Index: src/js/_enqueues/lib/ajax-response.js
===================================================================
--- src/js/_enqueues/lib/ajax-response.js	(revision 53089)
+++ src/js/_enqueues/lib/ajax-response.js	(working copy)
@@ -50,19 +50,28 @@
 				parsed.responses.push( response );
 			} );
 			if ( err.length ) {
-				re.html( '<div class="error">' + err + '</div>' );
+				re.html( '<div class="notice notice-error">' + err + '</div>' );
 				wp.a11y.speak( err );
 			} else if ( successmsg.length ) {
-				re.html( '<div class="updated notice is-dismissible"><p>' + successmsg + '</p></div>');
+				re.html( '<div class="notice notice-success is-dismissible"><p>' + successmsg + '</p></div>');
 				jQuery(document).trigger( 'wp-updates-notice-added' );
 				wp.a11y.speak( successmsg );
 			}
 			return parsed;
 		}
-		if ( isNaN(x) ) { return !re.html('<div class="error"><p>' + x + '</p></div>'); }
-		x = parseInt(x,10);
-		if ( -1 === x ) { return !re.html('<div class="error"><p>' + wpAjax.noPerm + '</p></div>'); }
-		else if ( 0 === x ) { return !re.html('<div class="error"><p>' + wpAjax.broken  + '</p></div>'); }
+		if ( isNaN( x ) ) {
+			wp.a11y.speak( x );
+			return ! re.html( '<div class="notice notice-error"><p>' + x + '</p></div>' );
+		}
+		x = parseInt( x, 10 );
+		if ( -1 === x ) {
+			wp.a11y.speak( wpAjax.noPerm );
+			return ! re.html( '<div class="notice notice-error"><p>' + wpAjax.noPerm + '</p></div>' );
+		}
+		else if ( 0 === x ) {
+			wp.a11y.speak( wpAjax.broken );
+			return ! re.html( '<div class="notice notice-error"><p>' + wpAjax.broken  + '</p></div>' );
+		}
 		return true;
 	},
 	invalidateForm: function ( selector ) {
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 53089)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -694,7 +694,7 @@
 
 	$scripts->add( 'clipboard', "/wp-includes/js/clipboard$suffix.js", array(), false, 1 );
 
-	$scripts->add( 'wp-ajax-response', "/wp-includes/js/wp-ajax-response$suffix.js", array( 'jquery' ), false, 1 );
+	$scripts->add( 'wp-ajax-response', "/wp-includes/js/wp-ajax-response$suffix.js", array( 'jquery', 'wp-a11y' ), false, 1 );
 	did_action( 'init' ) && $scripts->localize(
 		'wp-ajax-response',
 		'wpAjax',