diff --git a/xep-0260.xml b/xep-0260.xml
index 5e4e5b41..ff9a554f 100644
--- a/xep-0260.xml
+++ b/xep-0260.xml
@@ -656,7 +656,7 @@ Romeo                               Juliet
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
-      <xs:attribute name='sid' type='xs:string' use='optional'/>
+      <xs:attribute name='sid' type='xs:string' use='required'/>
     </xs:complexType>
   </xs:element>