diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index bbbffd9d5b..6b183c5ad9 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1054,7 +1054,8 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
         <returnvalue>numeric</returnvalue>
        </para>
        <para>
-        Factorial
+        Factorial (deprecated, will be removed in
+        <productname>PostgreSQL</productname> 14)
        </para>
        <para>
         <literal>5 !</literal>
@@ -1068,7 +1069,8 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
         <returnvalue>numeric</returnvalue>
        </para>
        <para>
-        Factorial (as a prefix operator)
+        Factorial (as a prefix operator; deprecated, will be removed in
+        <productname>PostgreSQL</productname> 14)
        </para>
        <para>
         <literal>!! 5</literal>
diff --git a/doc/src/sgml/ref/create_operator.sgml b/doc/src/sgml/ref/create_operator.sgml
index d5c385c087..2d265f34ef 100644
--- a/doc/src/sgml/ref/create_operator.sgml
+++ b/doc/src/sgml/ref/create_operator.sgml
@@ -92,6 +92,13 @@ CREATE OPERATOR <replaceable>name</replaceable> (
    unary operators only <literal>RIGHTARG</literal> should be defined.
   </para>
 
+  <note>
+   <para>
+    Right unary, also called postfix, operators are deprecated and will be
+    removed in <productname>PostgreSQL</productname> version 14.
+   </para>
+  </note>
+
   <para>
    The <replaceable class="parameter">function_name</replaceable>
    function must have been previously defined using <command>CREATE