diff --git a/includes/mail.inc b/includes/mail.inc
index 7a1d29ed..0275922 100644
--- a/includes/mail.inc
+++ b/includes/mail.inc
@@ -10,7 +10,7 @@
  *
  * $conf['mail_line_endings'] will override this setting.
  */
-define('MAIL_LINE_ENDINGS', isset($_SERVER['WINDIR']) || strpos($_SERVER['SERVER_SOFTWARE'], 'Win32') !== FALSE ? "\r\n" : "\n");
+define('MAIL_LINE_ENDINGS', isset($_SERVER['WINDIR']) || (isset($_SERVER['SERVER_SOFTWARE']) && strpos($_SERVER['SERVER_SOFTWARE'], 'Win32') !== FALSE) ? "\r\n" : "\n");
 
 /**
  * Composes and optionally sends an e-mail message.