Unclear "error" message when type parameter satisfying alias

[xkr47]

alias Foo => String|Integer;
void foo<T>(T t) given T satisfies Foo {}

.. gives the "error" for Foo on line 2:

Satisfies a type alias: 'Foo'

This is unclear and does not tell:

• why it's wrong
• what can be done

[xkr47]

Also, it wouid be handy if it actually wasn't an error :)