diff --git a/PhpOffice/PhpWord/Shared/ZipArchive.php b/PhpOffice/PhpWord/Shared/ZipArchive.php
index bc71e74..a5ed939 100644
--- a/PhpOffice/PhpWord/Shared/ZipArchive.php
+++ b/PhpOffice/PhpWord/Shared/ZipArchive.php
@@ -133,7 +133,7 @@ class ZipArchive
 
         if (!$this->usePclzip) {
             $zip = new \ZipArchive();
-            $result = $zip->open($this->filename, $flags);
+            $result = $zip->open($this->filename, $flags ?? 0);
 
             // Scrutizer will report the property numFiles does not exist
             // See https://github.com/scrutinizer-ci/php-analyzer/issues/190