diff --git a/shibboleth.php b/shibboleth.php
index 3c4b522..d19df90 100644
--- a/shibboleth.php
+++ b/shibboleth.php
@@ -148,7 +148,7 @@ function shibboleth_admin_hooks() {
 function shibboleth_session_active() { 
 	$active = false;
 
-	$session_headers = array('Shib-Session-ID', 'Shib_Session_ID', 'HTTP_SHIB_IDENTITY_PROVIDER');
+	$session_headers = array('Shib-Session-ID', 'Shib_Session_ID', 'SHIB_SESSION_ID', 'HTTP_SHIB_IDENTITY_PROVIDER');
 	foreach ($session_headers as $header) {
 		if ( array_key_exists($header, $_SERVER) && !empty($_SERVER[$header]) ) {
 			$active = true;