diff --git a/src/Processors/AugmentTags.php b/src/Processors/AugmentTags.php
index 22a2e49f..46006599 100644
--- a/src/Processors/AugmentTags.php
+++ b/src/Processors/AugmentTags.php
@@ -17,7 +17,7 @@ class AugmentTags implements ProcessorInterface
 {
 
     /** @var array<string> */
-    protected $whitelist = [];
+    protected array $whitelist = [];
 
     public function __construct(array $whitelist = [])
     {