Anonymous Namespace Ambiguity

Consider the following snippet:

void Foo() // 1
{
}

namespace
{
  void Foo() // 2
  {
  }
}

int main()
{
  Foo(); // Ambiguous.
  ::Foo(); // Calls the Foo in the global namespace (Foo #1).

  // I'm trying to call the `Foo` that's defined in the anonymous namespace (Foo #2).
}

How can I refer to something inside an anonymous namespace in this case?