diff --git a/src/Crate/PDO/Exception/InvalidArgumentException.php b/src/Crate/PDO/Exception/InvalidArgumentException.php
index b90c463a..5662ad0e 100644
--- a/src/Crate/PDO/Exception/InvalidArgumentException.php
+++ b/src/Crate/PDO/Exception/InvalidArgumentException.php
@@ -26,7 +26,7 @@
 
 class InvalidArgumentException extends PDOException implements ExceptionInterface
 {
-    public function __construct($message = 'Invalid argument', $code = 0, Exception $previous = null)
+    public function __construct($message = 'Invalid argument', $code = 0, ?Exception $previous = null)
     {
         parent::__construct($message, $code, $previous);
     }
diff --git a/src/Crate/PDO/Exception/UnsupportedException.php b/src/Crate/PDO/Exception/UnsupportedException.php
index e96c612b..a77cc445 100644
--- a/src/Crate/PDO/Exception/UnsupportedException.php
+++ b/src/Crate/PDO/Exception/UnsupportedException.php
@@ -28,7 +28,7 @@
 
 class UnsupportedException extends PDOException
 {
-    public function __construct($message = 'Unsupported functionality', $code = 0, Exception $previous = null)
+    public function __construct($message = 'Unsupported functionality', $code = 0, ?Exception $previous = null)
     {
         parent::__construct($message, $code, $previous);
     }
diff --git a/src/Crate/PDO/Http/ServerPool.php b/src/Crate/PDO/Http/ServerPool.php
index 806b3981..bd83f612 100644
--- a/src/Crate/PDO/Http/ServerPool.php
+++ b/src/Crate/PDO/Http/ServerPool.php
@@ -72,7 +72,7 @@ final class ServerPool implements ServerInterface
      * @param array $servers
      * @param ClientInterface|null $client
      */
-    public function __construct(array $servers, ClientInterface $client = null)
+    public function __construct(array $servers, ?ClientInterface $client = null)
     {
         if (\count($servers) === 0) {
             $servers = [self::DEFAULT_SERVER];
diff --git a/src/Crate/PDO/PDOStatementImplementationPhp8.php b/src/Crate/PDO/PDOStatementImplementationPhp8.php
index 557410e2..9c1c5501 100644
--- a/src/Crate/PDO/PDOStatementImplementationPhp8.php
+++ b/src/Crate/PDO/PDOStatementImplementationPhp8.php
@@ -37,7 +37,8 @@ trait PDOStatementImplementationPhp8
      *
      * @return bool
      */
-    public function setFetchMode(int $mode, ...$args)
+    #[\ReturnTypeWillChange]
+    public function setFetchMode(int $mode, ...$args): bool
     {
         return $this->doSetFetchMode($mode, ...$args);
     }
@@ -51,7 +52,7 @@ public function setFetchMode(int $mode, ...$args)
      * @return mixed[]
      */
     #[\ReturnTypeWillChange]
-    public function fetchAll(int $mode = null, ...$args)
+    public function fetchAll(?int $mode = null, ...$args)
     {
         return $this->doFetchAll($mode, ...$args);
     }