diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 78dc3fa..6e431eb 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -222,6 +222,8 @@ jobs:
           - "8.0"
           - "8.1"
           - "8.2"
+          - "8.3"
+          - "8.4"
 
     steps:
       - name: krb5-dev
diff --git a/src/Exception/Exception.php b/src/Exception/Exception.php
index 2c4bb12..199cdf3 100644
--- a/src/Exception/Exception.php
+++ b/src/Exception/Exception.php
@@ -12,7 +12,7 @@
  * @psalm-consistent-constructor
  */
 class Exception extends \Exception {
-	public function __construct(string $message = "", int $code = 0, Throwable $previous = null) {
+	public function __construct(string $message = "", int $code = 0, ?Throwable $previous = null) {
 		parent::__construct($message, $code, $previous);
 	}
 
diff --git a/src/Exception/InvalidRequestException.php b/src/Exception/InvalidRequestException.php
index 1212420..d6ee8db 100644
--- a/src/Exception/InvalidRequestException.php
+++ b/src/Exception/InvalidRequestException.php
@@ -12,7 +12,7 @@ class InvalidRequestException extends Exception {
 	 */
 	protected $path;
 
-	public function __construct(string $path = "", int $code = 0, \Throwable $previous = null) {
+	public function __construct(string $path = "", int $code = 0, ?\Throwable $previous = null) {
 		$class = get_class($this);
 		$parts = explode('\\', $class);
 		$baseName = array_pop($parts);
diff --git a/src/ServerFactory.php b/src/ServerFactory.php
index 28f0180..ee7e5af 100644
--- a/src/ServerFactory.php
+++ b/src/ServerFactory.php
@@ -33,9 +33,9 @@ class ServerFactory {
 	 * @param ITimeZoneProvider|null $timeZoneProvider
 	 */
 	public function __construct(
-		IOptions $options = null,
-		ISystem $system = null,
-		ITimeZoneProvider $timeZoneProvider = null
+		?IOptions $options = null,
+		?ISystem $system = null,
+		?ITimeZoneProvider $timeZoneProvider = null
 	) {
 		if (is_null($options)) {
 			$options = new Options();