Alter column...using failure under 9.0.4

Dear list,

I’ve a strange issue here. I’ve a table that I’m sure the column type is boolean. I can see the datatype is boolean on PgAdmin.

Nevertheless, when I issue this command

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alter table usuario alter column ativo type smallint using (case when ativo then 1 else 0 end);

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I get the following error:

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ERROR:  argument of IS FALSE must be type boolean, not type smallint

********** Error **********

ERROR: argument of IS FALSE must be type boolean, not type smallint

SQL state: 42804

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I already run Vacuum just to be sure, but still not working.

I have a script with hundred similar lines (for other tables) without any error, just this table.

Any hints?

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