diff --git a/src/PhpSpreadsheet/Writer/Html.php b/src/PhpSpreadsheet/Writer/Html.php
index f3b40fa1..eb50c456 100644
--- a/src/PhpSpreadsheet/Writer/Html.php
+++ b/src/PhpSpreadsheet/Writer/Html.php
@@ -136,7 +136,7 @@ class Html extends BaseWriter
      *
      * @var null|callable
      */
-    protected $editHtmlCallback;
+    private $editHtmlCallback;
 
     /**
      * Create a new HTML.