diff --git a/src/Connector.php b/src/Connector.php
index 456a3d1..c7b0ac3 100644
--- a/src/Connector.php
+++ b/src/Connector.php
@@ -15,7 +15,7 @@ class Connector {
     protected $_connector;
     protected $_negotiator;
 
-    public function __construct(LoopInterface $loop = null, ConnectorInterface $connector = null) {
+    public function __construct(?LoopInterface $loop = null, ?ConnectorInterface $connector = null) {
         $this->_loop = $loop ?: Loop::get();
 
         if (null === $connector) {
diff --git a/src/functions.php b/src/functions.php
index 373afe4..b060fd8 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -9,7 +9,7 @@
  * @param LoopInterface|null $loop
  * @return \React\Promise\PromiseInterface<\Ratchet\Client\WebSocket>
  */
-function connect($url, array $subProtocols = [], $headers = [], LoopInterface $loop = null) {
+function connect($url, array $subProtocols = [], $headers = [], ?LoopInterface $loop = null) {
     $connector = new Connector($loop);
     $connection = $connector($url, $subProtocols, $headers);