diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 62711ee83f..8921907f5e 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -12492,8 +12492,9 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
        <structfield>off</structfield> <type>int8</type>
       </para>
       <para>
-       The offset at which the allocation starts. NULL for anonymous
-       allocations and unused memory.
+       The offset at which the allocation starts. For anonymous allocations,
+       no information about individual allocations is available, so the column
+       will be NULL in that case.
       </para></entry>
      </row>