diff --git a/class.phpmailer.php b/class.phpmailer.php
index 38bb3ce79..f2a57ad27 100644
--- a/class.phpmailer.php
+++ b/class.phpmailer.php
@@ -3411,8 +3411,8 @@ public function DKIM_Add($headers_line, $subject, $body)
                 $to_header = $header;
                 $current = 'to_header';
             } else {
-                if ($current && strpos($header, ' =?') === 0) {
-                    $current .= $header;
+                if ($$current && strpos($header, ' =?') === 0) {
+                    $$current .= $header;
                 } else {
                     $current = '';
                 }