diff --git a/class.phpmailer.php b/class.phpmailer.php
index 916e69ab..35ad763e 100644
--- a/class.phpmailer.php
+++ b/class.phpmailer.php
@@ -602,10 +602,16 @@ class PHPMailer
      */
     private function mailPassthru($to, $subject, $body, $header, $params)
     {
-        if (ini_get('safe_mode') || !($this->UseSendmailOptions)) {
-            $rt = @mail($to, $this->encodeHeader($this->secureHeader($subject)), $body, $header);
+        //Check overloading of mail function to avoid double-encoding
+        if (ini_get('mbstring.func_overload') & 1) {
+            $subject = $this->secureHeader($subject);
         } else {
-            $rt = @mail($to, $this->encodeHeader($this->secureHeader($subject)), $body, $header, $params);
+            $subject = $this->encodeHeader($this->secureHeader($subject));
+        }
+        if (ini_get('safe_mode') || !($this->UseSendmailOptions)) {
+            $rt = @mail($to, $subject, $body, $header);
+        } else {
+            $rt = @mail($to, $subject, $body, $header, $params);
         }
         return $rt;
     }