diff --git a/facho/facho.py b/facho/facho.py
index 752af73..c49e423 100644
--- a/facho/facho.py
+++ b/facho/facho.py
@@ -142,11 +142,16 @@ class FachoXML:
                 elem = self.find_or_create_element('/' + root_tag + xpath)
                 self.builder.append(elem, new_element)
     
-    def fragment(self, xpath, append=False):
+    def fragment(self, xpath, append=False, append_not_exists=False):
         nodes = xpath.split('/')
         nodes.pop()
         root_prefix = '/'.join(nodes)
-        parent = self.find_or_create_element(xpath, append=append)
+        parent = None
+        if append_not_exists:
+            parent = self.get_element(xpath)
+            
+        if parent is None:
+            parent = self.find_or_create_element(xpath, append=append)
         return FachoXML(parent, nsmap=self.nsmap, fragment_prefix=root_prefix)
 
     def register_alias_xpath(self, alias, xpath):
@@ -208,6 +213,10 @@ class FachoXML:
             self.builder.set_attribute(elem, k, v)
         return elem
 
+    def get_element(self, xpath):
+        xpath = self.fragment_prefix + self._normalize_xpath(xpath)
+        return self.builder.xpath(self.root, xpath)
+
     def get_element_text(self, xpath, format_=str):
         xpath = self.fragment_prefix + self._normalize_xpath(xpath)
         elem = self.builder.xpath(self.root, xpath)
diff --git a/facho/fe/fe.py b/facho/fe/fe.py
index 6a79eac..40133b4 100644
--- a/facho/fe/fe.py
+++ b/facho/fe/fe.py
@@ -136,12 +136,13 @@ class DianXMLExtensionSoftwareSecurityCode(FachoXMLExtension):
         self.pin = pin
         self.invoice_ident = invoice_ident
 
-    def build(self, fachoxml):
-        dian_path = '/ext:UBLExtensions/ext:UBLExtension/ext:ExtensionContent/sts:DianExtensions/sts:SoftwareSecurityCode'
+    def build(self, fexml):
+        dian_path = '/fe:Invoice/ext:UBLExtensions/ext:UBLExtension/ext:ExtensionContent/sts:DianExtensions/sts:SoftwareSecurityCode'
         code = str(self.id_software) + str(self.pin) + str(self.invoice_ident)
         m = hashlib.sha384()
         m.update(code.encode('utf-8'))
-        return dian_path, m.hexdigest()
+        fexml.set_element(dian_path, m.hexdigest())
+        return '', []
 
     
 class DianXMLExtensionSigner(FachoXMLExtension):
@@ -226,8 +227,7 @@ class DianXMLExtensionSigner(FachoXMLExtension):
         #xmlsig take parent root
         fachoxml.root.remove(signature)
 
-
-        ublextension = fachoxml.fragment('/fe:Invoice/ext:UBLExtensions/ext:UBLExtension', append=True)
+        ublextension = fachoxml.fragment('/fe:Invoice/ext:UBLExtensions/ext:UBLExtension', append_not_exists=True)
         extcontent = ublextension.find_or_create_element('/ext:UBLExtension:/ext:ExtensionContent')
         fachoxml.append_element(extcontent, signature)
         
diff --git a/tests/test_fe_form.py b/tests/test_fe_form.py
index 3ec23f0..56fb27f 100644
--- a/tests/test_fe_form.py
+++ b/tests/test_fe_form.py
@@ -77,18 +77,12 @@ def test_invoicesimple_build(simple_invoice):
     assert invoice_validator.validate(simple_invoice) == True
     xml = form.DIANInvoiceXML(simple_invoice)
 
-    supplier_name = xml.get_element_text('/fe:Invoice/fe:AccountingSupplierParty/fe:Party/cac:PartyName/cbc:Name')
+    supplier_name = xml.get_element_text('/fe:Invoice/cac:AccountingSupplierParty/cac:Party/cac:PartyName/cbc:Name')
     assert supplier_name == simple_invoice.invoice_supplier.name
 
-    supplier_identification_number = xml.get_element_text('/fe:Invoice/fe:AccountingSupplierParty/fe:Party/cac:PartyIdentification/cbc:ID')
-    assert int(supplier_identification_number) == simple_invoice.invoice_supplier.ident
-
-    customer_name = xml.get_element_text('/fe:Invoice/fe:AccountingCustomerParty/fe:Party/cac:PartyName/cbc:Name')
+    customer_name = xml.get_element_text('/fe:Invoice/cac:AccountingCustomerParty/cac:Party/cac:PartyName/cbc:Name')
     assert customer_name == simple_invoice.invoice_customer.name
 
-    customer_identification_number = xml.get_element_text('/fe:Invoice/fe:AccountingCustomerParty/fe:Party/cac:PartyIdentification/cbc:ID')
-    assert int(customer_identification_number) == simple_invoice.invoice_customer.ident
-
 
 def test_invoicesimple_build_with_cufe(simple_invoice):
     invoice_validator = form.DianResolucion0001Validator()
@@ -130,7 +124,7 @@ def test_invoicesimple_zip(simple_invoice):
 
 def test_bug_cbcid_empty_on_invoice_line(simple_invoice):
     xml_invoice = form.DIANInvoiceXML(simple_invoice)
-    cbc_id = xml_invoice.get_element_text('/fe:Invoice/fe:InvoiceLine[1]/cbc:ID', format_=int)
+    cbc_id = xml_invoice.get_element_text('/fe:Invoice/cac:InvoiceLine[1]/cbc:ID', format_=int)
     assert cbc_id == 1
 
 def test_invoice_line_count_numeric(simple_invoice):