diff --git a/lib/SimpleSAML/SessionHandlerPHP.php b/lib/SimpleSAML/SessionHandlerPHP.php
index 8b7008c700af67eb18c3efb856fef28459b09aad..c1832f20a6e1a76583468d410c0958fbc06c086e 100644
--- a/lib/SimpleSAML/SessionHandlerPHP.php
+++ b/lib/SimpleSAML/SessionHandlerPHP.php
@@ -372,7 +372,7 @@ class SessionHandlerPHP extends SessionHandler
             session_set_cookie_params(
                 $cookieParams['lifetime'],
                 $cookieParams['path'],
-                $cookieParams['domain'],
+                $cookieParams['domain'] ?? '',
                 $cookieParams['secure'],
                 $cookieParams['httponly']
             );