Index: wp-includes/class-phpmailer.php
===================================================================
--- wp-includes/class-phpmailer.php	(revision 18073)
+++ wp-includes/class-phpmailer.php	(working copy)
@@ -451,7 +451,7 @@
    */
   private function AddAnAddress($kind, $address, $name = '') {
     if (!preg_match('/^(to|cc|bcc|ReplyTo)$/', $kind)) {
-      echo 'Invalid recipient array: ' . kind;
+      echo 'Invalid recipient array: ' . $kind;
       return false;
     }
     $address = trim($address);