diff --git a/src/Ratchet/Server/IoServer.php b/src/Ratchet/Server/IoServer.php
index c89a85a..45b66fe 100644
--- a/src/Ratchet/Server/IoServer.php
+++ b/src/Ratchet/Server/IoServer.php
@@ -54,7 +54,7 @@ class IoServer {
      * @param  string                             $address    The address to receive sockets on (0.0.0.0 means receive connections from any)
      * @return IoServer
      */
-    public static function factory(MessageComponentInterface $component, integer|null $port = null, string|null $address = null) {
+    public static function factory(MessageComponentInterface $component, ?int $port = null, ?string $address = null) {
         if ($port == null) $port = 80;
         if ($address == null) $address = '0.0.0.0';