diff --git a/wp-includes/class-phpmailer.php b/wp-includes/class-phpmailer.php
index 4589cd791..21a0d0c30 100644
--- a/wp-includes/class-phpmailer.php
+++ b/wp-includes/class-phpmailer.php
@@ -757,7 +757,7 @@ class PHPMailer {
    * @return bool
    */
   protected function SmtpSend($header, $body) {
-    require_once $this->PluginDir . 'class.smtp.php';
+    require_once $this->PluginDir . 'class-smtp.php';
     $bad_rcpt = array();
 
     if(!$this->SmtpConnect()) {