--- /dev/null
+--TEST--
+Bug #20564 Unsetting headers
+--SKIPIF--
+--FILE--
+<?php
+include("Mail/mime.php");
+
+$mime = new Mail_mime;
+$mime->setSubject('test');
+
+$headers = $mime->headers(array('Subject' => null), true);
+echo array_key_exists('Subject', $headers) ? '1' : '0';
+--EXPECT--
+0
\ No newline at end of file