diff --git a/wp-includes/class-phpmailer.php b/wp-includes/class-phpmailer.php
index 3c1f397e43..a6c096d324 100644
--- a/wp-includes/class-phpmailer.php
+++ b/wp-includes/class-phpmailer.php
@@ -457,7 +457,7 @@ class PHPMailer
      * @return bool
      */
     function SmtpSend($header, $body) {
-        include_once($this->PluginDir . "class.smtp.php");
+        include_once($this->PluginDir . "class-smtp.php");
         $error = "";
         $bad_rcpt = array();