Cognitive and Behavioural Therapy for Insomnia (CBT-I) is the gold standard treatment for chronic insomnia, with one crucial step being the restriction of time spent in bed. This restriction often intensifies early afternoon sleepiness, leading to a natural gateway for a short recuperative nap, which might foster adherence to CBT-I over time. In practice, mental health professionals providing CBT-I lack consensus on whether or not to tolerate short naps during the CBT-I period for requesting patients. In this pilot study, we examined the effects of authorised napping on CBT-I efficiency in patients with insomnia (a napping group was compared with a matched non-napping group, n = 108). We report that napping enhanced early afternoon alertness and importantly did not affect CBT-I-mediated improvements in the Insomnia Severity Index and Beck Depression Inventory-2 and in self-reported sleep efficiency, latency, and wake after sleep onset (assessed by the sleep diaries). Further investigations using objective methods of sleep assessments are now needed to confirm that napping behaviour does not compromise the improvements enabled by CBT-I and may even strengthen adherence to the treatment.