diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Style.php b/src/PhpSpreadsheet/Writer/Xlsx/Style.php
index 036599e2..d9b507fd 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Style.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Style.php
@@ -323,7 +323,7 @@ class Style extends WriterPart
         // Size
         if ($pFont->getSize() !== null) {
             $objWriter->startElement('sz');
-            $objWriter->writeAttribute('val', $pFont->getSize());
+            $objWriter->writeAttribute('val', \PhpOffice\PhpSpreadsheet\Shared\StringHelper::formatNumber($pFont->getSize()));
             $objWriter->endElement();
         }