diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index b620feb..916ca79 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -969,6 +969,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
          <entry>Waiting to read or truncate multixact information.</entry>
         </row>
         <row>
+         <entry><literal>OldSnapshotTimeMapLock</></entry>
+         <entry>Waiting to read or update old snapshot control
+		 information.</entry>
+        </row>
+        <row>
          <entry morerows="15"><literal>LWLockTranche</></entry>
          <entry><literal>clog</></entry>
          <entry>Waiting for I/O on a clog (transaction status) buffer.</entry>