Private modifier for F# types

If we have

module M

type private A = B | C

(...)

The private modifier means that A will only be usable from within the module M. But in this case:

namespace N

type private A = B | C

(...)

What will be the effect of that private modifier? It doesn't make sense for a CLR namespace to have private members, as the namespace can be extended at will, so will that private modifier have any effect at all?