diff --git a/test/Invoice-unit-UBL/BR-CO-19.xml b/test/Invoice-unit-UBL/BR-CO-19.xml
index 448cc8be..553e2920 100644
--- a/test/Invoice-unit-UBL/BR-CO-19.xml
+++ b/test/Invoice-unit-UBL/BR-CO-19.xml
@@ -73,4 +73,21 @@
 		</Invoice>
 	</test>
 	
+	<test>
+		<assert>
+			<description>Verify that BT-8 can be informed even if there is no Invoice period defined.</description>
+			<success>BR-CO-19</success>
+		</assert>
+		<Invoice
+			xmlns:cac="urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2"
+			xmlns:cbc="urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2"
+			xmlns="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2">
+			<cac:InvoicePeriod>
+				<!--<cbc:StartDate>2013-06-01</cbc:StartDate>
+				<cbc:EndDate>2013-06-30</cbc:EndDate>-->
+                <cbc:DescriptionCode>3</cbc:DescriptionCode>  
+			</cac:InvoicePeriod>
+			
+		</Invoice>
+	</test>
 </testSet>
diff --git a/ubl/schematron/UBL/EN16931-UBL-model.sch b/ubl/schematron/UBL/EN16931-UBL-model.sch
index aa2e2908..185d3686 100644
--- a/ubl/schematron/UBL/EN16931-UBL-model.sch
+++ b/ubl/schematron/UBL/EN16931-UBL-model.sch
@@ -76,7 +76,7 @@
   <param name="BR-CO-13" value="((cbc:ChargeTotalAmount) and (cbc:AllowanceTotalAmount) and (xs:decimal(cbc:TaxExclusiveAmount) = round((xs:decimal(cbc:LineExtensionAmount) + xs:decimal(cbc:ChargeTotalAmount) - xs:decimal(cbc:AllowanceTotalAmount)) * 10 * 10) div 100 ))  or (not(cbc:ChargeTotalAmount) and (cbc:AllowanceTotalAmount) and (xs:decimal(cbc:TaxExclusiveAmount) = round((xs:decimal(cbc:LineExtensionAmount) - xs:decimal(cbc:AllowanceTotalAmount)) * 10 * 10 ) div 100)) or ((cbc:ChargeTotalAmount) and not(cbc:AllowanceTotalAmount) and (xs:decimal(cbc:TaxExclusiveAmount) = round((xs:decimal(cbc:LineExtensionAmount) + xs:decimal(cbc:ChargeTotalAmount)) * 10 * 10 ) div 100)) or (not(cbc:ChargeTotalAmount) and not(cbc:AllowanceTotalAmount) and (xs:decimal(cbc:TaxExclusiveAmount) = xs:decimal(cbc:LineExtensionAmount)))"/>
   <param name="BR-CO-14" value="(xs:decimal(child::cbc:TaxAmount)= round((sum(cac:TaxSubtotal/xs:decimal(cbc:TaxAmount)) * 10 * 10)) div 100) or not(cac:TaxSubtotal)"/>
   <param name="BR-CO-15" value="every $Currency in cbc:DocumentCurrencyCode satisfies (cac:LegalMonetaryTotal/xs:decimal(cbc:TaxInclusiveAmount) = round( (cac:LegalMonetaryTotal/xs:decimal(cbc:TaxExclusiveAmount) + cac:TaxTotal/xs:decimal(cbc:TaxAmount[@currencyID=$Currency])) * 10 * 10) div 100)"/>
-  <param name="BR-CO-16" value="(exists(cbc:PrepaidAmount) and not(exists(cbc:PayableRoundingAmount)) and (xs:decimal(cbc:PayableAmount) = (round((xs:decimal(cbc:TaxInclusiveAmount) - xs:decimal(cbc:PrepaidAmount)) * 10 * 10) div 100))) or (not(xs:decimal(cbc:PrepaidAmount)) and not(xs:decimal(cbc:PayableRoundingAmount)) and xs:decimal(cbc:PayableAmount) = xs:decimal(cbc:TaxInclusiveAmount)) or (xs:decimal(cbc:PrepaidAmount) and xs:decimal(cbc:PayableRoundingAmount) and ((round((xs:decimal(cbc:PayableAmount) - xs:decimal(cbc:PayableRoundingAmount)) * 10 * 10) div 100) = (round((xs:decimal(cbc:TaxInclusiveAmount) - xs:decimal(cbc:PrepaidAmount)) * 10 * 10) div 100))) or (not(xs:decimal(cbc:PrepaidAmount)) and xs:decimal(cbc:PayableRoundingAmount) and ((round((xs:decimal(cbc:PayableAmount) - xs:decimal(cbc:PayableRoundingAmount)) * 10 * 10) div 100) = xs:decimal(cbc:TaxInclusiveAmount))) "/>
+  <param name="BR-CO-16" value="(exists(cbc:PrepaidAmount) and not(exists(cbc:PayableRoundingAmount)) and (xs:decimal(cbc:PayableAmount) = (round((xs:decimal(cbc:TaxInclusiveAmount) - xs:decimal(cbc:PrepaidAmount)) * 10 * 10) div 100))) or (not(exists(cbc:PrepaidAmount)) and not(exists(cbc:PayableRoundingAmount)) and xs:decimal(cbc:PayableAmount) = xs:decimal(cbc:TaxInclusiveAmount)) or (exists(cbc:PrepaidAmount) and exists(cbc:PayableRoundingAmount) and ((round((xs:decimal(cbc:PayableAmount) - xs:decimal(cbc:PayableRoundingAmount)) * 10 * 10) div 100) = (round((xs:decimal(cbc:TaxInclusiveAmount) - xs:decimal(cbc:PrepaidAmount)) * 10 * 10) div 100))) or  (not(exists(cbc:PrepaidAmount)) and exists(cbc:PayableRoundingAmount) and ((round((xs:decimal(cbc:PayableAmount) - xs:decimal(cbc:PayableRoundingAmount)) * 10 * 10) div 100) = xs:decimal(cbc:TaxInclusiveAmount)))"/>
   <param name="BR-CO-17" value="(round(cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/xs:decimal(cbc:Percent)) = 0 and (round(xs:decimal(cbc:TaxAmount)) = 0)) or (round(cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/xs:decimal(cbc:Percent)) != 0 and ((abs(xs:decimal(cbc:TaxAmount)) - 1 &lt; round(abs(xs:decimal(cbc:TaxableAmount)) * (cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/xs:decimal(cbc:Percent) div 100) * 10 * 10) div 100 ) and (abs(xs:decimal(cbc:TaxAmount)) + 1 &gt; round(abs(xs:decimal(cbc:TaxableAmount)) * (cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/xs:decimal(cbc:Percent) div 100) * 10 * 10) div 100 )))  or (not(exists(cac:TaxCategory[cac:TaxScheme/normalize-space(upper-case(cbc:ID))='VAT']/xs:decimal(cbc:Percent))) and (round(xs:decimal(cbc:TaxAmount)) = 0))"/>
   <param name="BR-CO-18" value="exists(cac:TaxTotal/cac:TaxSubtotal)"/>
   <param name="BR-CO-19" value="exists(cbc:StartDate) or exists(cbc:EndDate) or (exists(cbc:DescriptionCode) and not(exists(cbc:StartDate)) and not(exists(cbc:EndDate)))"/>