To estimate an environmental property such as object location from multiple sensory cues, the brain must infer their causal relationship. Only cues originating from the same source should be integrated. This inference relies on the characteristics of the cues as well as on a cross-modal common-cause prior: accumulated knowledge about the probability that cross-modal cues come from the same source. We examined the plasticity of this cross-modal common-cause prior. In a learning phase, participants were exposed to a series of audiovisual stimuli that were either consistently spatiotemporally congruent or consistently incongruent; participants’ audiovisual spatial integration was measured before and after this exposure. We fitted several Bayesian causal-inference models to the data; the models differed in the plasticity of the common-source prior. Model comparison revealed that, for the majority of the participants, the common-cause prior changed during the learning phase. Our findings reveal that short periods of exposure to audiovisual stimuli with a consistent causal relationship can modify the common-cause prior. In accordance with previous studies, both exposure conditions could either strengthen or weaken the common-cause prior at the participant-level. Simulations imply that the direction of the prior update might be mediated by the perceptual variability of the cues during the learning phase.