PostgreSQL syntax question

The following syntax (which is legal under Oracle) does not parse under
PostreSQL 6.3.2.

 update table1 set col1=(select col2 from table2 where col3='x') where col4='z';

Is there a variant of the syntax which does work?

Cheers and thanks,
Stephen.

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Stephen Davies Consulting                                            scldad@sdc.com.au
Adelaide, South Australia.                                             Voice: 61-8-82728863
Computing & Network solutions.                                     Fax: 61-8-82741015