In the Tractatus Wittgenstein argued that there are metaphysical truths. But these are ineffable, for metaphysical sentences try to say what can only be shown. Accordingly, they are pseudo-propositions because they are ill-formed. In the Investigations he no longer thought that metaphysical propositions are pseudo-propositions, but argued that they are either nonsense or norms of descriptions. Popper criticized Wittgenstein's ideas and argued that metaphysical truths are effable. Yet it is by now clear that he misunderstood Wittgenstein's arguments (namely that metaphysical propositions are ill-formed because they employ unbound variables) and misguidedly thought that Wittgenstein used the principle of verification for distinguishing empirical propositions from metaphysical propositions. Because Popper developed his philosophy in part as a critique of Wittgenstein's philosophy, this invites the question of whether these misunderstandings have consequences for his own philosophy. I discuss this question and argue that Popper's attempt to distinguish metaphysics and science with the aid of a criterion of testability is from Wittgenstein's perspective misguided. The main problem facing Popper's philosophy is that alleged metaphysical propositions are not theoretical propositions but rules for descriptions (in the misleading guise of empirical propositions). If Wittgenstein's ideas are correct, then metaphysical problems are not scientific but grammatical problems which can only be resolved through conceptual investigations.