Index: src/wp-login.php
===================================================================
--- src/wp-login.php	(revision 43389)
+++ src/wp-login.php	(working copy)
@@ -28,7 +28,7 @@
  * @param string   $title    Optional. WordPress login Page title to display in the `<title>` element.
  *                           Default 'Log In'.
  * @param string   $message  Optional. Message to display in header. Default empty.
- * @param WP_Error $wp_error Optional. The error to pass. Default empty.
+ * @param WP_Error $wp_error Optional. The error to pass. Default is a new empty error.
  */
 function login_header( $title = 'Log In', $message = '', $wp_error = '' ) {
 	global $error, $interim_login, $action;
@@ -38,7 +38,7 @@
 
 	add_action( 'login_head', 'wp_login_viewport_meta' );
 
-	if ( empty( $wp_error ) ) {
+	if ( ! is_wp_error( $wp_error ) ) {
 		$wp_error = new WP_Error();
 	}