diff --git a/lib/SimpleSAML/Session.php b/lib/SimpleSAML/Session.php
index bb70f47445fba2d648e9d40d8ac567b5e388eeaa..7ddd48b605bd7da83cefe95c76c2244dcee84712 100644
--- a/lib/SimpleSAML/Session.php
+++ b/lib/SimpleSAML/Session.php
@@ -444,6 +444,7 @@ class SimpleSAML_Session {
 		$this->authority = NULL;
 		$this->attributes = NULL;
 		$this->logoutState = NULL;
+		$this->idp = NULL;
 
 		/* Delete data which expires on logout. */
 		$this->expireDataLogout();