diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 5c6092e424..55a5a63ae5 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.273 2005/07/29 14:46:56 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.274 2005/07/30 14:52:04 momjian Exp $
 PostgreSQL documentation
 -->
 
@@ -4903,6 +4903,24 @@ SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
    such pair.
   </para>
 
+  <para>
+   When adding an <type>interval</type> value to (or subtracting an 
+   <type>interval</type> value from) a <type>timestamp with time zone</type> 
+   value, the days component advances (or decrements) the date of the 
+   <type>timestamp with time zone<type> by the indicated number of days. 
+   Across daylight saving time changes (with the session tiem zone set to a 
+   time zone that recognizes DST), this means <literal>interval '1 day'</literal> 
+   does not necessarily equal <literal>interval '24 hours'</literal>. 
+   For example, with the session time zone set to <literal>CST7CDT</literal>
+   <literal>timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' </literal>
+   will produce <literal>timestamp with time zone '2005-04-03 12:00-06'</literal>, 
+   while adding <literal>interval '24 hours'</literal> to the same initial 
+   <type>timestamp with time zone</type> produces
+   <literal>timestamp with time zone '2005-04-03 13:00-06'</literal>, as there is
+   a change in daylight saving time at <literal>2005-04-03 02:00</literal> in time zone 
+   <literal>CST7CDT</literal>.
+  </para>
+
     <table id="operators-datetime-table">
      <title>Date/Time Operators</title>
 
diff --git a/src/test/regress/expected/horology.out b/src/test/regress/expected/horology.out
index c0a7f6e5b8..fe85c2dfcf 100644
--- a/src/test/regress/expected/horology.out
+++ b/src/test/regress/expected/horology.out
@@ -598,6 +598,33 @@ SELECT (timestamp with time zone 'tomorrow' > 'now') as "True";
  t
 (1 row)
 
+-- timestamp with time zone, interval arithmetic around DST change
+SET TIME ZONE 'CST7CDT';
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' as "Apr 3, 12:00";
+         Apr 3, 12:00         
+------------------------------
+ Sun Apr 03 12:00:00 2005 CDT
+(1 row)
+
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '24 hours' as "Apr 3, 13:00";
+         Apr 3, 13:00         
+------------------------------
+ Sun Apr 03 13:00:00 2005 CDT
+(1 row)
+
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '1 day' as "Apr 2, 12:00";
+         Apr 2, 12:00         
+------------------------------
+ Sat Apr 02 12:00:00 2005 CST
+(1 row)
+
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '24 hours' as "Apr 2, 11:00";
+         Apr 2, 11:00         
+------------------------------
+ Sat Apr 02 11:00:00 2005 CST
+(1 row)
+
+RESET TIME ZONE;
 SELECT timestamptz(date '1994-01-01', time '11:00') AS "Jan_01_1994_10am";
        Jan_01_1994_10am       
 ------------------------------
diff --git a/src/test/regress/expected/interval.out b/src/test/regress/expected/interval.out
index 7480e7f2e5..9efcdf8139 100644
--- a/src/test/regress/expected/interval.out
+++ b/src/test/regress/expected/interval.out
@@ -228,3 +228,16 @@ select '4 millenniums 5 centuries 4 decades 1 year 4 months 4 days 17 minutes 31
  @ 4541 years 4 mons 4 days 17 mins 31 secs
 (1 row)
 
+-- test justify_hours() and justify_days()
+SELECT justify_hours(interval '6 months 3 days 52 hours 3 minutes 2 seconds') as "6 mons 5 days 4 hours 3 mins 2 seconds";
+ 6 mons 5 days 4 hours 3 mins 2 seconds 
+----------------------------------------
+ @ 6 mons 5 days 4 hours 3 mins 2 secs
+(1 row)
+
+SELECT justify_days(interval '6 months 36 days 5 hours 4 minutes 3 seconds') as "7 mons 6 days 5 hours 4 mins 3 seconds";
+ 7 mons 6 days 5 hours 4 mins 3 seconds 
+----------------------------------------
+ @ 7 mons 6 days 5 hours 4 mins 3 secs
+(1 row)
+
diff --git a/src/test/regress/sql/horology.sql b/src/test/regress/sql/horology.sql
index afc9feb0c8..d4be1f51d5 100644
--- a/src/test/regress/sql/horology.sql
+++ b/src/test/regress/sql/horology.sql
@@ -114,6 +114,15 @@ SELECT (timestamp with time zone 'today' = (timestamp with time zone 'tomorrow'
 SELECT (timestamp with time zone 'tomorrow' = (timestamp with time zone 'yesterday' + interval '2 days')) as "True";
 SELECT (timestamp with time zone 'tomorrow' > 'now') as "True";
 
+-- timestamp with time zone, interval arithmetic around DST change
+SET TIME ZONE 'CST7CDT';
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' as "Apr 3, 12:00";
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '24 hours' as "Apr 3, 13:00";
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '1 day' as "Apr 2, 12:00";
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '24 hours' as "Apr 2, 11:00";
+RESET TIME ZONE;
+
+
 SELECT timestamptz(date '1994-01-01', time '11:00') AS "Jan_01_1994_10am";
 SELECT timestamptz(date '1994-01-01', time '10:00') AS "Jan_01_1994_9am";
 SELECT timestamptz(date '1994-01-01', time with time zone '11:00-8') AS "Jan_01_1994_11am";
diff --git a/src/test/regress/sql/interval.sql b/src/test/regress/sql/interval.sql
index cd17ebbc95..25e58659e7 100644
--- a/src/test/regress/sql/interval.sql
+++ b/src/test/regress/sql/interval.sql
@@ -69,3 +69,10 @@ select avg(f1) from interval_tbl;
 
 -- test long interval input
 select '4 millenniums 5 centuries 4 decades 1 year 4 months 4 days 17 minutes 31 seconds'::interval;
+
+
+-- test justify_hours() and justify_days()
+
+SELECT justify_hours(interval '6 months 3 days 52 hours 3 minutes 2 seconds') as "6 mons 5 days 4 hours 3 mins 2 seconds";
+SELECT justify_days(interval '6 months 36 days 5 hours 4 minutes 3 seconds') as "7 mons 6 days 5 hours 4 mins 3 seconds";
+