Ant : from path to fileset

I'd like to convert a path to a fileset. I need it to use in "copy" task.

I define my path like that:

<path id="classpath">
<pathelement location="${lib.dir}\activation.jar" />
<pathelement location="${lib.dir}\mail.jar" />
...
</path>

I need to copy all this to the jar directory:

<copy todir="${dist.lib.dir}" >
<fileset refid="classpath" />
</copy>

But i have the error:

BUILD FAILED
build.xml:83: classpath doesn't denote a fileset

How can i do that ?

.