diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
new file mode 100644
index 67bae32..cc54cc8
*** a/doc/src/sgml/datatype.sgml
--- b/doc/src/sgml/datatype.sgml
*************** P <optional> <replaceable>years</replace
*** 2671,2689 ****
      </para>
  
      <para>
-      Internally <type>interval</type> values are stored as months, days,
-      and seconds. This is done because the number of days in a month
-      varies, and a day can have 23 or 25 hours if a daylight savings
-      time adjustment is involved.  The months and days fields are integers
-      while the seconds field can store fractions.  Because intervals are
-      usually created from constant strings or <type>timestamp</type> subtraction,
-      this storage method works well in most cases. Functions
-      <function>justify_days</function> and <function>justify_hours</function> are
-      available for adjusting days and hours that overflow their normal
-      ranges.
-     </para>
- 
-     <para>
       In the verbose input format, and in some fields of the more compact
       input formats, field values can have fractional parts; for example
       <literal>'1.5 week'</literal> or <literal>'01:02:03.45'</literal>.  Such input is
--- 2671,2676 ----
*************** P <optional> <replaceable>years</replace
*** 2734,2739 ****
--- 2721,2753 ----
        </tgroup>
       </table>
  
+     <para>
+      Internally <type>interval</type> values are stored as months, days,
+      and seconds. This is done because the number of days in a month
+      varies, and a day can have 23 or 25 hours if a daylight savings
+      time adjustment is involved.  The months and days fields are integers
+      while the seconds field can store fractions.  Because intervals are
+      usually created from constant strings or <type>timestamp</type> subtraction,
+      this storage method works well in most cases, but can cause unexpected
+      results:
+ 
+ <programlisting>
+ SELECT EXTRACT(hours from '80 minutes'::interval);
+  date_part
+ -----------
+          1
+ 
+ SELECT EXTRACT(days from '80 hours'::interval);
+  date_part
+ -----------
+          0
+ </programlisting>
+ 
+      Functions <function>justify_days</function> and
+      <function>justify_hours</function> are available for adjusting days
+      and hours that overflow their normal ranges.
+     </para>
+ 
     </sect2>
  
     <sect2 id="datatype-interval-output">