diff --git a/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php b/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php
index d2f5bc3..325cc3d 100644
--- a/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php
+++ b/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php
@@ -12,13 +12,10 @@ class StyleRegistry
 {
     /** @var array [SERIALIZED_STYLE] => [STYLE_ID] mapping table, keeping track of the registered styles */
     protected $serializedStyleToStyleIdMappingTable = [];
-    protected $serializedNumberFormatToFormatIdMappingTable = [];
 
     /** @var array [STYLE_ID] => [STYLE] mapping table, keeping track of the registered styles */
     protected $styleIdToStyleMappingTable = [];
 
-    protected $numberFormats = [];
-
     /**
      * @param Style $defaultStyle
      */
diff --git a/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php b/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php
index f83f16b..0a72ba9 100644
--- a/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php
+++ b/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php
@@ -72,8 +72,9 @@ EOD;
 
         $content = '<numFmts count="'.count($registeredFormats).'">';
         /** @var NumberFormat $format */
-        foreach ($registeredFormats as $format) {
-
+        foreach ($registeredFormats as $styleId) {
+            $style = $this->styleRegistry->getStyleFromStyleId($styleId);
+            $format = $style->getNumberFormat();
             $content .= '<numFmt numFmtId="'.$format->getId().'" formatCode="'.$format->getFormatCode().'"/>';
         }
         $content .= '</numFmts>';