Parenting stress in mothers of children with autism spectrum disorder (ASD) is high and impacts perceptions about parenting. This study examined the relationship between parenting stress and observer-perceived limit-setting ability. Participants’ perceptions of other parents’ limit-setting ability were assessed by showing participants video clips of parenting behaviours. Mothers of 93 children with autism spectrum disorder completed an online survey regarding the severity of their own child’s autism spectrum disorder (Social Communication Questionnaire), their child’s behaviour problems (Strengths and Difficulties Questionnaire) and their own levels of parenting stress (Questionnaire on Resources and Stress). They were shown five videos of other parents interacting with children with autism spectrum disorder and were asked to rate the limit-setting abilities observed in each video using the Parent–Child Relationship Inventory. Higher parenting stress negatively related to judgements about others’ limit-setting skills. This mirrors the literature regarding the relationship between self-reported parenting stress and rating child behaviour more negatively. It suggests that stress negatively impacts a wide range of judgements and implies that caution may be required when interpreting the results of studies in which parenting skills are assessed by self-report.