diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index b5f67af..61a21a9 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -161,6 +161,8 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
         <literal>INCLUDING</> clause, which can slightly reduce the size of the index,
         due to storing included attributes only in leaf index pages.
         Currently, only the B-tree access method supports this feature.
+        Expressions as included columns are not supported since they cannot be used
+        in index-only scan.
        </para>
       </listitem>
      </varlistentry>