diff --git a/lib/SimpleSAML/Session.php b/lib/SimpleSAML/Session.php
index 9507b66b072a558c6ca56a9279ca93678cf02583..9845355a45dfd6de070a2e33efc77addb5678b63 100644
--- a/lib/SimpleSAML/Session.php
+++ b/lib/SimpleSAML/Session.php
@@ -507,6 +507,10 @@ class SimpleSAML_Session implements SimpleSAML_ModifiedInfo {
 	 */
 	private function expireData() {
 
+		if(!is_array($this->dataStore)) {
+			return;
+		}
+
 		$ct = time();
 
 		foreach($this->dataStore as &$typedData) {