diff --git a/src/Exceptions/InvalidUserProvider.php b/src/Exceptions/InvalidUserProvider.php
index b1feeb7..c7c6498 100644
--- a/src/Exceptions/InvalidUserProvider.php
+++ b/src/Exceptions/InvalidUserProvider.php
@@ -6,7 +6,7 @@
 
 class InvalidUserProvider extends \Exception
 {
-    public function __construct(string $guard, $message = "", $code = 0, Throwable $previous = null)
+    public function __construct(string $guard, $message = "", $code = 0, ?Throwable $previous = null)
     {
         parent::__construct(sprintf('Invalid user provider for guard %s', $guard), $code, $previous);
     }
diff --git a/src/Exceptions/MissingUserProvider.php b/src/Exceptions/MissingUserProvider.php
index 618814f..3a53fab 100644
--- a/src/Exceptions/MissingUserProvider.php
+++ b/src/Exceptions/MissingUserProvider.php
@@ -6,7 +6,7 @@
 
 class MissingUserProvider extends \Exception
 {
-    public function __construct(string $guard, $message = "", $code = 0, Throwable $previous = null)
+    public function __construct(string $guard, $message = "", $code = 0, ?Throwable $previous = null)
     {
         parent::__construct(sprintf('Missing user provider for guard %s', $guard), $code, $previous);
     }