diff --git a/lib/SimpleSAML/SessionHandlerPHP.php b/lib/SimpleSAML/SessionHandlerPHP.php
index 53ba9d5132fe6059a11db8f6cd6dda5d66de23df..8b7008c700af67eb18c3efb856fef28459b09aad 100644
--- a/lib/SimpleSAML/SessionHandlerPHP.php
+++ b/lib/SimpleSAML/SessionHandlerPHP.php
@@ -97,7 +97,7 @@ class SessionHandlerPHP extends SessionHandler
                 session_set_cookie_params(
                     $params['lifetime'],
                     $params['path'],
-                    $params['domain'],
+                    $params['domain'] ?? '',
                     $params['secure'],
                     $params['httponly']
                 );