diff --git a/src/Exception/NotComparableException.php b/src/Exception/NotComparableException.php
index cf1165f..50838dd 100644
--- a/src/Exception/NotComparableException.php
+++ b/src/Exception/NotComparableException.php
@@ -13,7 +13,7 @@ class NotComparableException extends LogicException
      * @param mixed          $rhs
      * @param Exception|null $previous
      */
-    public function __construct($lhs, $rhs, Exception $previous = null)
+    public function __construct($lhs, $rhs, ?Exception $previous = null)
     {
         parent::__construct(
             sprintf(