diff --git a/src/Db/Driver/Mysql.php b/src/Db/Driver/Mysql.php
index 6175e3afe..8f2d9505e 100644
--- a/src/Db/Driver/Mysql.php
+++ b/src/Db/Driver/Mysql.php
@@ -74,6 +74,7 @@ final class Mysql
                     );
                 }
 
+                assert($config instanceof MysqlConfig);
                 self::$connections[$dbKey] = [
                     new MysqlConnectionPool($config, $settings->getMaxConnections(), $settings->getIdleTimeout()),
                     $pdo