diff --git a/src/PhpSpreadsheet/Worksheet/PageSetup.php b/src/PhpSpreadsheet/Worksheet/PageSetup.php
index f52b414a..290b8349 100644
--- a/src/PhpSpreadsheet/Worksheet/PageSetup.php
+++ b/src/PhpSpreadsheet/Worksheet/PageSetup.php
@@ -823,7 +823,7 @@ class PageSetup
         return $this->setFirstPageNumber(null);
     }
 
-    public function getPageOrder(): string
+    public function getPageOrder(): ?string
     {
         return $this->pageOrder;
     }