diff --git a/phpstan.neon b/phpstan.neon
index 49cb743..d461cdd 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,5 @@
 parameters:
-  level: 8
+  level: 9
   paths:
     - src
     - tests
\ No newline at end of file
diff --git a/src/BaseClient.php b/src/BaseClient.php
index aa2058d..f68b2ab 100644
--- a/src/BaseClient.php
+++ b/src/BaseClient.php
@@ -18,7 +18,7 @@ public function __construct(
     /**
      * @deprecated 1.0 use Sysix\LexOffice\Utils::getJsonFromResponse()
      */
-    public function getAsJson(ResponseInterface $response): object
+    public function getAsJson(ResponseInterface $response): mixed
     {
         trigger_error(self::class . '::' . __METHOD__ . ' should not be called anymore, use \Sysix\LexOffice\Utils::getJsonFromResponse instead', E_USER_DEPRECATED);