diff --git a/src/Writers/UblWriter.php b/src/Writers/UblWriter.php
index 225873d..b807d4f 100644
--- a/src/Writers/UblWriter.php
+++ b/src/Writers/UblWriter.php
@@ -398,9 +398,11 @@ private function addSellerOrBuyerNode(UXML $parent, Party $party) {
         if ($taxRegistrationId !== null) {
             $taxRegistrationNode = $xml->add('cac:PartyTaxScheme');
             $taxRegistrationNode->add('cbc:CompanyID', $taxRegistrationId->getValue());
+
+            $taxRegistrationSchemeNode = $taxRegistrationNode->add('cac:TaxScheme');
             $taxRegistrationScheme = $taxRegistrationId->getScheme();
             if ($taxRegistrationScheme !== null) {
-                $taxRegistrationNode->add('cac:TaxScheme')->add('cbc:ID', $taxRegistrationScheme);
+                $taxRegistrationSchemeNode->add('cbc:ID', $taxRegistrationScheme);
             }
         }
 
diff --git a/tests/Writers/UblWriterTest.php b/tests/Writers/UblWriterTest.php
index 2623e10..5cd3336 100644
--- a/tests/Writers/UblWriterTest.php
+++ b/tests/Writers/UblWriterTest.php
@@ -38,6 +38,7 @@ private function getSampleInvoice(): Invoice {
         $seller = (new Party)
             ->setElectronicAddress(new Identifier('9482348239847239874', '0088'))
             ->setCompanyId(new Identifier('COMPANY_ID', '0183'))
+            ->setTaxRegistrationId(new Identifier('12345678')) // NOTE: Missing scheme on purpose
             ->setName('Seller Name Ltd.')
             ->setTradingName('Seller Name')
             ->setVatNumber('ESA00000000')