diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
index 0ee0cc7e64..974153cb78 100644
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -130,7 +130,10 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
       If the <literal>HAVING</literal> clause is present, it
       eliminates groups that do not satisfy the given condition.  (See
       <xref linkend="sql-groupby"/> and
-      <xref linkend="sql-having"/> below.)
+      <xref linkend="sql-having"/> below.)  
+      Although query output columns are nominally computed in the next
+      step, they can also be referenced (by name or ordinal number)
+      in the <literal>GROUP BY</literal> clause.
      </para>
     </listitem>