diff --git wp-includes/functions.php wp-includes/functions.php
index 0e720ee..cc4886c 100644
--- wp-includes/functions.php
+++ wp-includes/functions.php
@@ -2815,6 +2815,12 @@ function _xmlrpc_wp_die_handler( $message, $title = '', $args = array() ) {
  * @param string $message Optional. Response to print. Default empty.
  */
 function _ajax_wp_die_handler( $message = '' ) {
+	if ( function_exists( 'is_wp_error' ) && is_wp_error( $message ) ) {
+		$errors = $message->get_error_messages();
+		if ( 0 < count( $errors ) ) {
+			$message = join( ', ', $errors );
+		}
+	}
 	if ( is_scalar( $message ) )
 		die( (string) $message );
 	die( '0' );