diff --git a/src/exceptions/SQLException.php b/src/exceptions/SQLException.php
index a0e15cf..269efd0 100644
--- a/src/exceptions/SQLException.php
+++ b/src/exceptions/SQLException.php
@@ -23,7 +23,7 @@ public function __construct(
         array $params = [],
         string $message = 'SQL Error',
         int $code = 0,
-        Exception $previous = null
+        Exception|null $previous = null
     ) {
         parent::__construct(
             "{$message}\n" . QueryFormatter::formatQuery($sql, $params),
diff --git a/src/framework/Connection.php b/src/framework/Connection.php
index a771212..ae43177 100644
--- a/src/framework/Connection.php
+++ b/src/framework/Connection.php
@@ -72,7 +72,7 @@ public function transact(callable $func): bool;
      *
      * @return string|int|null the last auto-generated ID (usually an integer, could be a string for UUIDs, etc.)
      */
-    public function lastInsertId(?string $sequence_name = null): string|int|null;
+    public function lastInsertId(string|null $sequence_name = null): string|int|null;
 
     /**
      * Add a `Logger` instance, which will be notified when a query is executed.
diff --git a/src/framework/pdo/PDOConnection.php b/src/framework/pdo/PDOConnection.php
index 1a9c667..6138271 100644
--- a/src/framework/pdo/PDOConnection.php
+++ b/src/framework/pdo/PDOConnection.php
@@ -217,7 +217,7 @@ private function expandPlaceholders(string $sql, array $params): string
     /**
      * @param $sequence_name auto-sequence name (or NULL for e.g. MySQL which supports only one auto-key)
      */
-    public function lastInsertId(?string $sequence_name = null): string|int|null
+    public function lastInsertId(string|null $sequence_name = null): string|int|null
     {
         $id = $this->pdo->lastInsertId($sequence_name);
         
diff --git a/src/framework/pdo/PDOProvider.php b/src/framework/pdo/PDOProvider.php
index 609d949..91fb331 100644
--- a/src/framework/pdo/PDOProvider.php
+++ b/src/framework/pdo/PDOProvider.php
@@ -49,7 +49,7 @@ class PDOProvider
      * @param string|null            $host     optional hostname; defaults to "localhost"
      * @param int|null               $port     optional port-number; defaults to the standard port-number for the given $db type
      */
-    public function __construct(string $protocol, string $dbname, string $username, string $password, array $options = null, string $host = null, int|null $port = null)
+    public function __construct(string $protocol, string $dbname, string $username, string $password, array|null $options = null, string|null $host = null, int|null $port = null)
     {
         static $default_port = [
             self::PROTOCOL_MYSQL    => 3306,
diff --git a/src/model/Database.php b/src/model/Database.php
index 0668a3a..900a921 100644
--- a/src/model/Database.php
+++ b/src/model/Database.php
@@ -18,7 +18,7 @@ abstract class Database
      *
      * @param DatabaseContainerFactory|null $factory custom factory instance (typically omitted)
      */
-    public function __construct(DatabaseContainerFactory $factory = null)
+    public function __construct(DatabaseContainerFactory|null $factory = null)
     {
         if ($factory === null) {
             $factory = new DatabaseContainerFactory();
diff --git a/src/model/components/Returning.php b/src/model/components/Returning.php
index 5af62a4..636d306 100644
--- a/src/model/components/Returning.php
+++ b/src/model/components/Returning.php
@@ -52,7 +52,7 @@ public function returningColumns($cols): static
      *
      * @return $this
      */
-    public function returningValue($expr, $name = null, $type = null): static
+    public function returningValue(string $expr, string|null $name = null, Type|string|null $type = null): static
     {
         $this->return_vars->addValue($expr, $name, $type);
 
diff --git a/src/model/query/SelectQuery.php b/src/model/query/SelectQuery.php
index 77bfaee..2824b89 100644
--- a/src/model/query/SelectQuery.php
+++ b/src/model/query/SelectQuery.php
@@ -119,7 +119,7 @@ public function columns(Column|array $cols)
      *
      * @return $this
      */
-    public function value($expr, $name = null, $type = null)
+    public function value(string $expr, string|null $name = null, Type|string|null $type = null)
     {
         $this->return_vars->addValue($expr, $name, $type);
 
diff --git a/test/helpers.php b/test/helpers.php
index 6beb60b..c8df055 100644
--- a/test/helpers.php
+++ b/test/helpers.php
@@ -22,7 +22,7 @@ function normalize_sql($sql)
  * @param string      $expected_sql
  * @param string|null $why
  */
-function sql_eq(Statement $query, $expected_sql, $why = null)
+function sql_eq(Statement $query, $expected_sql, string|null $why = null)
 {
     $actual = normalize_sql($query->getSQL());
     $expected = normalize_sql($expected_sql);