diff --git a/source/modules/MEI.cmn.xml b/source/modules/MEI.cmn.xml
index c57feca1c..047eedec6 100644
--- a/source/modules/MEI.cmn.xml
+++ b/source/modules/MEI.cmn.xml
@@ -384,6 +384,9 @@
           <valItem ident="ligature">
             <desc xml:lang="en">Represents a ligature in the mensural notation source material.</desc>
           </valItem>
+          <valItem ident="unspecified">
+            <desc xml:lang="en">Unspecified bracket.</desc>
+          </valItem>
         </valList>
       </attDef>
     </attList>