Multicolumn indexes and ORDER BY

I have a multicolumn index on two columns. If i use the columns in ORDER BY
like this:
ORDER BY col1, col2;

The index is used. But, if one column is sorted DESC it is not used:
ORDER BY col1 DESC, col2;

How can i make this work ?

Regards,
Jernej Kos.
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Kostko <kostko(at)jweb-network(dot)net>
JWeb-Network