diff --git a/lib/phpmailer/class.phpmailer.php b/lib/phpmailer/class.phpmailer.php
index 0752dbd81f9..f640cdfb12a 100644
--- a/lib/phpmailer/class.phpmailer.php
+++ b/lib/phpmailer/class.phpmailer.php
@@ -1155,7 +1155,7 @@ class PHPMailer
     /// Start Moodle Hack - if we are running under unicodedb, we'll try our own
     /// encode_header code that's multibyte-safe
         global $CFG;
-        if ($CFG->unicodedb) {
+        if (!empty($CFG->unicodedb)) {
             $textlib = textlib_get_instance();
             return $textlib->encode_mimeheader($str, $this->CharSet);
         }