Including diffraction modelling in an acoustic simulation is known to improve the plausibility of rendered room acoustics in Virtual Reality (VR). In VR, acoustic rendering only needs to satisfy the expectations raised by the visual room impression. In Augmented Reality (AR), however, the user’s natural acoustic environment provides an additional reference, which typically increases the perceptual demands. This study assesses a selection of diffraction modelling approaches in an augmented reality (AR) setting in an L-shaped corridor. The participants rated the plausibility and similarity using a paired-comparison paradigm. Comparisons were included between acoustic simulations and between simulations and a real sound source. This is, to the best of the authors’ knowledge, the first experiment investigating diffraction perception in an AR context. The results indicated that room auralisation including diffraction was rated as more plausible than auralisation without, similar to VR experiments. However, the real sound source was rated as more plausible than all of the simulations. These observations suggest that the relative performance of room acoustic modelling is perceived similarly in VR and AR experiments, but needs further improvement to be suitable for occlusion scenarios in AR, where diffraction modelling might not be the main limitation. In general, perceptually accurate acoustic modelling of a complex real environment remains a challenge in AR.