diff --git a/config.default.php b/config.default.php
index ad260cf10..40dfc2c1c 100644
--- a/config.default.php
+++ b/config.default.php
@@ -52,7 +52,7 @@ define('MAIL_SMTP_HOSTNAME', '');
 define('MAIL_SMTP_PORT', 25);
 define('MAIL_SMTP_USERNAME', '');
 define('MAIL_SMTP_PASSWORD', '');
-define('MAIL_SMTP_ENCRYPTION', null); // Valid values are "null", "ssl" or "tls"
+define('MAIL_SMTP_ENCRYPTION', null); // Valid values are null (not a string "null"), "ssl" or "tls"
 
 // Sendmail command to use when the transport is "sendmail"
 define('MAIL_SENDMAIL_COMMAND', '/usr/sbin/sendmail -bs');