diff --git a/resources/schema/inventory.xsd b/resources/schema/inventory.xsd
index 59417f3..d1b6b15 100644
--- a/resources/schema/inventory.xsd
+++ b/resources/schema/inventory.xsd
@@ -254,6 +254,7 @@
         </xsd:attribute>
         <xsd:attribute name="sloleks" type="xsd:string"/> <!-- Sloleks ID -->
         <xsd:attribute name="kol" type="xsd:string"/> <!-- legacy attribute for the word's lemma -->
+        <xsd:attribute name="lexical_unit_lexeme_id" type="xsd:int"/> <!-- ID within its lexical unit -->
       </xsd:extension>
     </xsd:simpleContent>
   </xsd:complexType>