A mysterious remark to Friedrich Waismann on 30 December 1929 marks the only occasion where Wittgenstein refers to both Heidegger and Kierkegaard. Yet although this has generated much controversy, little attention has been paid to the charge of nonsense that Wittgenstein here appears to bring against Heidegger; thus, the supporting argument that may be latent has not been unearthed. Through analysis of this remark, Wittgenstein's arguments in the Tractatus and 'A Lecture on Ethics', and Heidegger's account of anxiety (Angst) in Being and Time, I argue that we can extract an argument against the central question of Heidegger's philosophy: the question of being. To understand this, I examine the Kierkegaardian ideas employed by Wittgenstein and Heidegger and attempt to show that this argument can be partly understood in Kierkegaardian terms. I further argue that examining what Heidegger means by 'being' (Sein) shows that Wittgenstein's argument does not meet its target.