diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 513112a216..b4648321dc 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -956,7 +956,7 @@ CREATE TABLE tree (
 );
 </programlisting>
     A top-level node would have NULL <structfield>parent_id</structfield>,
-    but non-NULL <structfield>parent_id</structfield> entries would be
+    while non-NULL <structfield>parent_id</structfield> entries would be
     constrained to reference valid rows of the table.
    </para>