diff --git a/functions/datetime.xml b/functions/datetime.xml
index 096b017662..43b3ab1926 100644
--- a/functions/datetime.xml
+++ b/functions/datetime.xml
@@ -669,6 +669,11 @@ echo strftime ("Last day in Feb 2000 is: %d", $lastday);
       </programlisting>
      </example>
     </para>
+    <simpara>
+    Date with year, month and day equal to zero is considered illegal 
+    (otherwise it what be regarded as 30.11.1999, which would be strange
+     behaviour).
+    </simpara>
     <para>
      See also <function>date</function> and <function>time</function>.
     </para>