diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e0a0a1c1..fd322b8b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,6 +24,7 @@ jobs:
           - "8.1"
           - "8.2"
           - "8.3"
+          - "8.4"
         dependencies:
           - "highest"
         include:
diff --git a/README.md b/README.md
index 317d158a..4f2e349a 100644
--- a/README.md
+++ b/README.md
@@ -101,7 +101,7 @@ composer require cboden/ratchet:^0.4.4
 See also the [CHANGELOG](CHANGELOG.md) for details about version upgrades.
 
 This project aims to run on any platform and thus does not require any PHP
-extensions and supports running on legacy PHP 5.4 through PHP 8.3+ with limited support for newer PHP.
+extensions and supports running on legacy PHP 5.4 through current PHP 8+.
 It's *highly recommended to use the latest supported PHP version* for this project.
 
 See above note about [Reviving Ratchet](#reviving-ratchet) for newer PHP support.
diff --git a/src/Ratchet/App.php b/src/Ratchet/App.php
index d3de200a..f2fa55cc 100644
--- a/src/Ratchet/App.php
+++ b/src/Ratchet/App.php
@@ -57,16 +57,19 @@ class App {
     protected $_routeCounter = 0;
 
     /**
-     * @param string        $httpHost   HTTP hostname clients intend to connect to. MUST match JS `new WebSocket('ws://$httpHost');`
-     * @param int           $port       Port to listen on. If 80, assuming production, Flash on 843 otherwise expecting Flash to be proxied through 8843
-     * @param string        $address    IP address to bind to. Default is localhost/proxy only. '0.0.0.0' for any machine.
-     * @param LoopInterface $loop       Specific React\EventLoop to bind the application to. null will create one for you.
-     * @param array         $context
+     * @param string         $httpHost   HTTP hostname clients intend to connect to. MUST match JS `new WebSocket('ws://$httpHost');`
+     * @param int            $port       Port to listen on. If 80, assuming production, Flash on 843 otherwise expecting Flash to be proxied through 8843
+     * @param string         $address    IP address to bind to. Default is localhost/proxy only. '0.0.0.0' for any machine.
+     * @param ?LoopInterface $loop       Specific React\EventLoop to bind the application to. null will create one for you.
+     * @param array          $context
      */
-    public function __construct($httpHost = 'localhost', $port = 8080, $address = '127.0.0.1', LoopInterface $loop = null, $context = array()) {
+    public function __construct($httpHost = 'localhost', $port = 8080, $address = '127.0.0.1', $loop = null, $context = array()) {
         if (extension_loaded('xdebug') && getenv('RATCHET_DISABLE_XDEBUG_WARN') === false) {
             trigger_error('XDebug extension detected. Remember to disable this if performance testing or going live!', E_USER_WARNING);
         }
+        if ($loop !== null && !$loop instanceof LoopInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #4 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
 
         if (null === $loop) {
             $loop = LoopFactory::create();
diff --git a/src/Ratchet/Http/HttpServerInterface.php b/src/Ratchet/Http/HttpServerInterface.php
index 2c37c490..614fb52b 100644
--- a/src/Ratchet/Http/HttpServerInterface.php
+++ b/src/Ratchet/Http/HttpServerInterface.php
@@ -10,5 +10,6 @@ interface HttpServerInterface extends MessageComponentInterface {
      * @param \Psr\Http\Message\RequestInterface    $request null is default because PHP won't let me overload; don't pass null!!!
      * @throws \UnexpectedValueException if a RequestInterface is not passed
      */
-    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null);
+    #[HackSupportForPHP8] public function onOpen(ConnectionInterface $conn, ?RequestInterface $request = null); /*
+    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null); /**/
 }
diff --git a/src/Ratchet/Http/NoOpHttpServerController.php b/src/Ratchet/Http/NoOpHttpServerController.php
index 4f72e668..5bb1f8e6 100644
--- a/src/Ratchet/Http/NoOpHttpServerController.php
+++ b/src/Ratchet/Http/NoOpHttpServerController.php
@@ -4,7 +4,8 @@
 use Psr\Http\Message\RequestInterface;
 
 class NoOpHttpServerController implements HttpServerInterface {
-    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) {
+    #[HackSupportForPHP8] public function onOpen(ConnectionInterface $conn, ?RequestInterface $request = null) { /*
+    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) { /**/
     }
 
     public function onMessage(ConnectionInterface $from, $msg) {
diff --git a/src/Ratchet/Http/OriginCheck.php b/src/Ratchet/Http/OriginCheck.php
index 2bdc0f7c..257c847b 100644
--- a/src/Ratchet/Http/OriginCheck.php
+++ b/src/Ratchet/Http/OriginCheck.php
@@ -31,7 +31,8 @@ public function __construct(MessageComponentInterface $component, array $allowed
     /**
      * {@inheritdoc}
      */
-    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) {
+    #[HackSupportForPHP8] public function onOpen(ConnectionInterface $conn, ?RequestInterface $request = null) { /*
+    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) { /**/
         $header = (string)$request->getHeader('Origin')[0];
         $origin = parse_url($header, PHP_URL_HOST) ?: $header;
 
diff --git a/src/Ratchet/Http/Router.php b/src/Ratchet/Http/Router.php
index 2bd5942f..71e52f2c 100644
--- a/src/Ratchet/Http/Router.php
+++ b/src/Ratchet/Http/Router.php
@@ -26,7 +26,8 @@ public function __construct(UrlMatcherInterface $matcher) {
      * {@inheritdoc}
      * @throws \UnexpectedValueException If a controller is not \Ratchet\Http\HttpServerInterface
      */
-    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) {
+    #[HackSupportForPHP8] public function onOpen(ConnectionInterface $conn, ?RequestInterface $request = null) { /*
+    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) { /**/
         if (null === $request) {
             throw new \UnexpectedValueException('$request can not be null');
         }
diff --git a/src/Ratchet/Server/IoServer.php b/src/Ratchet/Server/IoServer.php
index 0e84ae41..194a3317 100644
--- a/src/Ratchet/Server/IoServer.php
+++ b/src/Ratchet/Server/IoServer.php
@@ -34,7 +34,11 @@ class IoServer {
      * @param \React\Socket\ServerInterface       $socket   The React socket server to run the Ratchet application off of
      * @param \React\EventLoop\LoopInterface|null $loop     The React looper to run the Ratchet application off of
      */
-    public function __construct(MessageComponentInterface $app, ServerInterface $socket, LoopInterface $loop = null) {
+    public function __construct(MessageComponentInterface $app, ServerInterface $socket, $loop = null) {
+        if ($loop !== null && !$loop instanceof LoopInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #3 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+
         if (false === strpos(PHP_VERSION, "hiphop")) {
             gc_enable();
         }
diff --git a/src/Ratchet/Session/SessionProvider.php b/src/Ratchet/Session/SessionProvider.php
index 44276c54..76364e2b 100644
--- a/src/Ratchet/Session/SessionProvider.php
+++ b/src/Ratchet/Session/SessionProvider.php
@@ -38,13 +38,16 @@ class SessionProvider implements HttpServerInterface {
     protected $_serializer;
 
     /**
-     * @param \Ratchet\Http\HttpServerInterface           $app
-     * @param \SessionHandlerInterface                    $handler
-     * @param array                                       $options
-     * @param \Ratchet\Session\Serialize\HandlerInterface $serializer
+     * @param \Ratchet\Http\HttpServerInterface            $app
+     * @param \SessionHandlerInterface                     $handler
+     * @param array                                        $options
+     * @param ?\Ratchet\Session\Serialize\HandlerInterface $serializer
      * @throws \RuntimeException
      */
-    public function __construct(HttpServerInterface $app, \SessionHandlerInterface $handler, array $options = array(), HandlerInterface $serializer = null) {
+    public function __construct(HttpServerInterface $app, \SessionHandlerInterface $handler, array $options = array(), $serializer = null) {
+        if ($serializer !== null && !$serializer instanceof HandlerInterface) { // manual type check to support legacy PHP < 7.1
+            throw new \InvalidArgumentException('Argument #4 ($serializer) expected null|Ratchet\Session\Serialize\HandlerInterface');
+        }
         $this->_app     = $app;
         $this->_handler = $handler;
         $this->_null    = new NullSessionHandler;
@@ -70,7 +73,8 @@ public function __construct(HttpServerInterface $app, \SessionHandlerInterface $
     /**
      * {@inheritdoc}
      */
-    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) {
+    #[HackSupportForPHP8] public function onOpen(ConnectionInterface $conn, ?RequestInterface $request = null) { /*
+    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) { /**/
         $sessionName = ini_get('session.name');
 
         $id = array_reduce($request->getHeader('Cookie'), function($accumulator, $cookie) use ($sessionName) {
diff --git a/src/Ratchet/WebSocket/WsServer.php b/src/Ratchet/WebSocket/WsServer.php
index 27795ca7..5a015d83 100644
--- a/src/Ratchet/WebSocket/WsServer.php
+++ b/src/Ratchet/WebSocket/WsServer.php
@@ -104,7 +104,8 @@ public function __construct(ComponentInterface $component) {
     /**
      * {@inheritdoc}
      */
-    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) {
+    #[HackSupportForPHP8] public function onOpen(ConnectionInterface $conn, ?RequestInterface $request = null) { /*
+    public function onOpen(ConnectionInterface $conn, RequestInterface $request = null) { /**/
         if (null === $request) {
             throw new \UnexpectedValueException('$request can not be null');
         }
diff --git a/tests/helpers/Ratchet/Mock/Component.php b/tests/helpers/Ratchet/Mock/Component.php
deleted file mode 100644
index e152988b..00000000
--- a/tests/helpers/Ratchet/Mock/Component.php
+++ /dev/null
@@ -1,35 +0,0 @@
-<?php
-namespace Ratchet\Mock;
-use Ratchet\MessageComponentInterface;
-use Ratchet\WebSocket\WsServerInterface;
-use Ratchet\ConnectionInterface;
-
-class Component implements MessageComponentInterface, WsServerInterface {
-    public $last = array();
-
-    public $protocols = array();
-
-    public function __construct(ComponentInterface $app = null) {
-        $this->last[__FUNCTION__] = func_get_args();
-    }
-
-    public function onOpen(ConnectionInterface $conn) {
-        $this->last[__FUNCTION__] = func_get_args();
-    }
-
-    public function onMessage(ConnectionInterface $from, $msg) {
-        $this->last[__FUNCTION__] = func_get_args();
-    }
-
-    public function onClose(ConnectionInterface $conn) {
-        $this->last[__FUNCTION__] = func_get_args();
-    }
-
-    public function onError(ConnectionInterface $conn, \Exception $e) {
-        $this->last[__FUNCTION__] = func_get_args();
-    }
-
-    public function getSubProtocols() {
-        return $this->protocols;
-    }
-}
diff --git a/tests/unit/AppTest.php b/tests/unit/AppTest.php
new file mode 100644
index 00000000..7e058e38
--- /dev/null
+++ b/tests/unit/AppTest.php
@@ -0,0 +1,17 @@
+<?php
+namespace Ratchet;
+
+use PHPUnit\Framework\TestCase;
+use Ratchet\App;
+
+class AppTest extends TestCase {
+    public function testCtorThrowsForInvalidLoop() {
+        if (method_exists($this, 'expectException')) {
+            $this->expectException('InvalidArgumentException');
+            $this->expectExceptionMessage('Argument #4 ($loop) expected null|React\EventLoop\LoopInterface');
+        } else {
+            $this->setExpectedException('InvalidArgumentException', 'Argument #4 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+        new App('localhost', 8080, '127.0.0.1', 'loop');
+    }
+}
diff --git a/tests/unit/Server/IoServerTest.php b/tests/unit/Server/IoServerTest.php
index f337f1ea..0264f3fc 100644
--- a/tests/unit/Server/IoServerTest.php
+++ b/tests/unit/Server/IoServerTest.php
@@ -39,6 +39,16 @@ public function setUpServer() {
         $this->server = new IoServer($this->app, $this->reactor, $loop);
     }
 
+    public function testCtorThrowsForInvalidLoop() {
+        if (method_exists($this, 'expectException')) {
+            $this->expectException('InvalidArgumentException');
+            $this->expectExceptionMessage('Argument #3 ($loop) expected null|React\EventLoop\LoopInterface');
+        } else {
+            $this->setExpectedException('InvalidArgumentException', 'Argument #3 ($loop) expected null|React\EventLoop\LoopInterface');
+        }
+        new IoServer($this->app, $this->reactor, 'loop');
+    }
+
     public function testOnOpen() {
         $this->app->expects($this->once())->method('onOpen')->with($this->isInstanceOf('Ratchet\\ConnectionInterface'));
 
diff --git a/tests/unit/Session/SessionComponentTest.php b/tests/unit/Session/SessionProviderTest.php
similarity index 89%
rename from tests/unit/Session/SessionComponentTest.php
rename to tests/unit/Session/SessionProviderTest.php
index 98077dad..2bec51b0 100644
--- a/tests/unit/Session/SessionComponentTest.php
+++ b/tests/unit/Session/SessionProviderTest.php
@@ -24,6 +24,16 @@ public function setUpProvider() {
         $this->_serv = new SessionProvider($this->_app, new NullSessionHandler);
     }
 
+    public function testCtorThrowsForInvalidSerializer() {
+        if (method_exists($this, 'expectException')) {
+            $this->expectException('InvalidArgumentException');
+            $this->expectExceptionMessage('Argument #4 ($serializer) expected null|Ratchet\Session\Serialize\HandlerInterface');
+        } else {
+            $this->setExpectedException('InvalidArgumentException', 'Argument #4 ($serializer) expected null|Ratchet\Session\Serialize\HandlerInterface');
+        }
+        new SessionProvider($this->_app, new NullSessionHandler(), [], 'serializer');
+    }
+
     /**
      * @after
      */