diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 3717d13fff..03c0193709 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -4174,12 +4174,13 @@ ALTER INDEX measurement_city_id_logdate_key
     <itemizedlist>
      <listitem>
       <para>
-       Unique constraints (and hence primary keys) on partitioned tables must
-       include all the partition key columns.  This limitation exists because
-       the individual indexes making up the constraint can only directly
-       enforce uniqueness within their own partitions; therefore, the
-       partition structure itself must guarantee that there are not
-       duplicates in different partitions.
+       To create a unique or primary key constraint on a partitioned table,
+       the partition keys must not include any expressions or function calls
+       and the constraint's columns must include all of the partition key
+       columns.  This limitation exists because the individual indexes making
+       up the constraint can only directly enforce uniqueness within their own
+       partitions; therefore, the partition structure itself must guarantee
+       that there are not duplicates in different partitions.
       </para>
      </listitem>