diff --git a/doc/src/sgml/ref/comment.sgml b/doc/src/sgml/ref/comment.sgml
index 5b43c56b133..a824b99f826 100644
--- a/doc/src/sgml/ref/comment.sgml
+++ b/doc/src/sgml/ref/comment.sgml
@@ -80,14 +80,16 @@ COMMENT ON
   <title>Description</title>
 
   <para>
-   <command>COMMENT</command> stores a comment about a database object.
+   <command>COMMENT</command> stores, replaces, or removes the comment on a
+   database object.
   </para>
 
   <para>
-   Only one comment string is stored for each object, so to modify a comment,
-   issue a new <command>COMMENT</command> command for the same object.  To remove a
-   comment, write <literal>NULL</literal> in place of the text string.
-   Comments are automatically dropped when their object is dropped.
+   Only one comment string is stored for each object.  Issuing a new
+   <command>COMMENT</command> command for the same object replaces the
+   existing comment.  Specifying <literal>NULL</literal> or an empty
+   string (<literal>''</literal>) removes the comment.  Comments are
+   automatically dropped when their object is dropped.
   </para>
 
   <para>
@@ -266,7 +268,8 @@ COMMENT ON
     <term><replaceable class="parameter">string_literal</replaceable></term>
     <listitem>
      <para>
-      The new comment contents, written as a string literal.
+      The new comment contents, written as a string literal.  An empty string
+      (<literal>''</literal>) removes the comment.
      </para>
     </listitem>
    </varlistentry>
@@ -275,7 +278,7 @@ COMMENT ON
     <term><literal>NULL</literal></term>
     <listitem>
      <para>
-      Write <literal>NULL</literal> to drop the comment.
+      Write <literal>NULL</literal> to remove the comment.
      </para>
     </listitem>
    </varlistentry>
@@ -362,6 +365,7 @@ COMMENT ON TRANSFORM FOR hstore LANGUAGE plpython3u IS 'Transform between hstore
 COMMENT ON TRIGGER my_trigger ON my_table IS 'Used for RI';
 COMMENT ON TYPE complex IS 'Complex number data type';
 COMMENT ON VIEW my_view IS 'View of departmental costs';
+COMMENT ON VIEW my_view IS NULL;
 </programlisting></para>
  </refsect1>
 
diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out
index c90d0e40145..739a6e5ebed 100644
--- a/src/test/regress/expected/create_index.out
+++ b/src/test/regress/expected/create_index.out
@@ -32,6 +32,20 @@ COMMENT ON INDEX six_wrong IS 'bad index';
 ERROR:  relation "six_wrong" does not exist
 COMMENT ON INDEX six IS 'good index';
 COMMENT ON INDEX six IS NULL;
+SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null;
+ six_comment_is_null 
+---------------------
+ t
+(1 row)
+
+COMMENT ON INDEX six IS 'add the comment back';
+COMMENT ON INDEX six IS ''; -- empty string removes the comment, same as NULL
+SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null;
+ six_comment_is_null 
+---------------------
+ t
+(1 row)
+
 --
 -- BTREE partial indices
 --
diff --git a/src/test/regress/expected/create_role.out b/src/test/regress/expected/create_role.out
index 46d4f9efe99..5d0f21820ed 100644
--- a/src/test/regress/expected/create_role.out
+++ b/src/test/regress/expected/create_role.out
@@ -102,6 +102,33 @@ CREATE ROLE regress_rolecreator CREATEROLE;
 CREATE ROLE regress_hasprivs CREATEROLE LOGIN INHERIT CONNECTION LIMIT 5;
 -- ok, we should be able to modify a role we created
 COMMENT ON ROLE regress_hasprivs IS 'some comment';
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NOT NULL AS has_comment;
+ has_comment 
+-------------
+ t
+(1 row)
+
+COMMENT ON ROLE regress_hasprivs IS NULL;
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NULL AS no_comment;
+ no_comment 
+------------
+ t
+(1 row)
+
+COMMENT ON ROLE regress_hasprivs IS 'add the comment back';
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NOT NULL AS has_comment;
+ has_comment 
+-------------
+ t
+(1 row)
+
+COMMENT ON ROLE regress_hasprivs IS ''; -- empty string removes the comment, same as NULL
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NULL AS no_comment;
+ no_comment 
+------------
+ t
+(1 row)
+
 ALTER ROLE regress_hasprivs RENAME TO regress_tenant;
 ALTER ROLE regress_tenant NOINHERIT NOLOGIN CONNECTION LIMIT 7;
 -- fail, we should be unable to modify a role we did not create
diff --git a/src/test/regress/sql/create_index.sql b/src/test/regress/sql/create_index.sql
index 24241a40cec..506bdd6c920 100644
--- a/src/test/regress/sql/create_index.sql
+++ b/src/test/regress/sql/create_index.sql
@@ -45,6 +45,10 @@ CREATE INDEX six ON shighway USING btree (name text_ops);
 COMMENT ON INDEX six_wrong IS 'bad index';
 COMMENT ON INDEX six IS 'good index';
 COMMENT ON INDEX six IS NULL;
+SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null;
+COMMENT ON INDEX six IS 'add the comment back';
+COMMENT ON INDEX six IS ''; -- empty string removes the comment, same as NULL
+SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null;
 
 --
 -- BTREE partial indices
diff --git a/src/test/regress/sql/create_role.sql b/src/test/regress/sql/create_role.sql
index 4491a28a8ae..b22f9c6f50a 100644
--- a/src/test/regress/sql/create_role.sql
+++ b/src/test/regress/sql/create_role.sql
@@ -92,6 +92,13 @@ CREATE ROLE regress_hasprivs CREATEROLE LOGIN INHERIT CONNECTION LIMIT 5;
 
 -- ok, we should be able to modify a role we created
 COMMENT ON ROLE regress_hasprivs IS 'some comment';
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NOT NULL AS has_comment;
+COMMENT ON ROLE regress_hasprivs IS NULL;
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NULL AS no_comment;
+COMMENT ON ROLE regress_hasprivs IS 'add the comment back';
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NOT NULL AS has_comment;
+COMMENT ON ROLE regress_hasprivs IS ''; -- empty string removes the comment, same as NULL
+SELECT shobj_description('regress_hasprivs'::regrole, 'pg_authid') IS NULL AS no_comment;
 ALTER ROLE regress_hasprivs RENAME TO regress_tenant;
 ALTER ROLE regress_tenant NOINHERIT NOLOGIN CONNECTION LIMIT 7;