diff --git a/system/Encryption/Handlers/SodiumHandler.php b/system/Encryption/Handlers/SodiumHandler.php
index b6c74da76581..c74f2a5f0a48 100644
--- a/system/Encryption/Handlers/SodiumHandler.php
+++ b/system/Encryption/Handlers/SodiumHandler.php
@@ -26,7 +26,7 @@ class SodiumHandler extends BaseHandler
     /**
      * Starter key
      *
-     * @var string
+     * @var string|null Null is used for buffer cleanup.
      */
     protected $key = '';