diff --git a/structure/syntax/ubl-despatch-advice.xml b/structure/syntax/ubl-despatch-advice.xml
index c30e3841..050ea9ea 100644
--- a/structure/syntax/ubl-despatch-advice.xml
+++ b/structure/syntax/ubl-despatch-advice.xml
@@ -1448,13 +1448,13 @@
 						<Description>Identifies the transport handling unit.</Description>
 						<Reference type="BUSINESS_TERM">tir16-061</Reference>
 						<Value type="EXAMPLE">173500538500000016</Value>
-						<Attribute>
+						<Attribute usage="optional">
 							<Term>schemeID</Term>
 							<Name>Scheme identifier</Name>
 							<Description>Scheme identifier for the handling unit identifier</Description>
 							<Reference type="CODE_LIST">TransportHandlingUnitIDschemID</Reference>
 							<Value type="EXAMPLE">SSCC</Value>
-					</Attribute>
+						</Attribute>
 
 					</Element>
 					<Element cardinality="0..1">