Individuals with Autism Spectrum Disorder (ASD) are thought to under-rely on prior knowledge in perceptual decision-making. This study examined whether this applies to decisions of attention allocation, of relevance for 'predictive-coding' accounts of ASD. In a visual search task, a salient but task-irrelevant distractor appeared with higher probability in one display half. Individuals with ASD learned to avoid 'attentional capture' by distractors in the probable region as effectively as control participants--indicating typical priors for deploying attention. However, capture by a 'surprising' distractor at an unlikely location led to greatly slowed identification of a subsequent target at that location--indicating that individuals with ASD attempt to control surprise (unexpected attentional capture) by over-regulating parameters in post-selective decision-making.