diff --git a/correios/client.py b/correios/client.py
index c862719..ed4ffb2 100644
--- a/correios/client.py
+++ b/correios/client.py
@@ -421,17 +421,17 @@ def _get_sender_info_element(self, posting_list):
         xml_utils.SubElement(sender_info, "numero_contrato", text=str(contract.number))
         xml_utils.SubElement(sender_info, "numero_diretoria", text=str(contract.regional_direction_number))
         xml_utils.SubElement(sender_info, "codigo_administrativo", text=str(posting_card.administrative_code))
-        xml_utils.SubElement(sender_info, "nome_remetente", cdata=sender.name)
-        xml_utils.SubElement(sender_info, "logradouro_remetente", cdata=sender.street)
-        xml_utils.SubElement(sender_info, "numero_remetente", cdata=sender.number)
-        xml_utils.SubElement(sender_info, "complemento_remetente", cdata=sender.complement)
-        xml_utils.SubElement(sender_info, "bairro_remetente", cdata=sender.neighborhood)
+        xml_utils.SubElement(sender_info, "nome_remetente", cdata=str(sender.name))
+        xml_utils.SubElement(sender_info, "logradouro_remetente", cdata=str(sender.street))
+        xml_utils.SubElement(sender_info, "numero_remetente", cdata=str(sender.number) or 'S/n')
+        xml_utils.SubElement(sender_info, "complemento_remetente", cdata=str(sender.complement))
+        xml_utils.SubElement(sender_info, "bairro_remetente", cdata=str(sender.neighborhood))
         xml_utils.SubElement(sender_info, "cep_remetente", cdata=str(sender.zip_code))
         xml_utils.SubElement(sender_info, "cidade_remetente", cdata=str(sender.city)[:30])
         xml_utils.SubElement(sender_info, "uf_remetente", cdata=str(sender.state))
         xml_utils.SubElement(sender_info, "telefone_remetente", cdata=sender.phone.short)
         xml_utils.SubElement(sender_info, "fax_remetente", cdata="")
-        xml_utils.SubElement(sender_info, "email_remetente", cdata=sender.email)
+        xml_utils.SubElement(sender_info, "email_remetente", cdata=str(sender.email))
         return sender_info
 
     def _get_shipping_label_element(self, shipping_label: ShippingLabel):
diff --git a/tests/test_client.py b/tests/test_client.py
index 4f6ce13..1b359d3 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -359,6 +359,17 @@ def test_sn_informed_on_receiver_number(posting_list, shipping_label):
     assert b"<numero_end_destinatario>S/N</numero_end_destinatario>" in xml
 
 
+@pytest.mark.skipif(not correios, reason="API Client support disabled")
+def test_sn_informed_on_sender_number(posting_list, shipping_label):
+    shipping_label.sender.raw_number = ''
+    posting_list.add_shipping_label(shipping_label)
+    serializer = correios.PostingListSerializer()
+    document = serializer.get_document(posting_list)
+    serializer.validate(document)
+    xml = serializer.get_xml(document)
+    assert b"<numero_remetente><![CDATA[S/N]]></numero_remetente>" in xml
+
+
 @pytest.mark.skipif(not correios, reason="API Client support disabled")
 def test_fail_empty_posting_list_serialization(posting_list):
     serializer = correios.PostingListSerializer()