diff --git a/src/JsonRPC/Exception/ResponseException.php b/src/JsonRPC/Exception/ResponseException.php
index e97b4e6..3d4d3b8 100644
--- a/src/JsonRPC/Exception/ResponseException.php
+++ b/src/JsonRPC/Exception/ResponseException.php
@@ -30,7 +30,7 @@ class ResponseException extends RpcCallFailedException
      * @param Exception $previous [optional] The previous exception used for the exception chaining. Since 5.3.0
      * @param mixed     $data     [optional] A value that contains additional information about the error.
      */
-    public function __construct($message = '', $code = 0, Exception $previous = null, $data = null)
+    public function __construct($message = '', $code = 0, ?Exception $previous = null, $data = null)
     {
         parent::__construct($message, $code, $previous);
         $this->setData($data);
diff --git a/src/JsonRPC/ProcedureHandler.php b/src/JsonRPC/ProcedureHandler.php
index 11b4a3b..1c0ca20 100644
--- a/src/JsonRPC/ProcedureHandler.php
+++ b/src/JsonRPC/ProcedureHandler.php
@@ -355,7 +355,7 @@ public function getNamedArguments(array $requestParams, array $methodParams)
      * @param SmdBuilder $SmdBuilder
      * @return array|string
      */
-    public function getSMD($target, $returnJSON = true, SmdBuilder $SmdBuilder = null) {
+    public function getSMD($target, $returnJSON = true, ?SmdBuilder $SmdBuilder = null) {
         if(!$SmdBuilder) {
             $SmdBuilder = new SmdBuilder();
         }