Battery-powered and energy-harvesting IEEE 802.15.4 nodes are subject to so-called denial-of-sleep attacks. Such attacks generally aim at draining the energy of a victim device. Especially, session key establishment schemes for IEEE 802.15.4 security are susceptible to denial-of-sleep attacks since injected requests for session key establishment typically trigger energy-consuming processing and communication. Nevertheless, Krentz et al.’s Adaptive Key Establishment Scheme (AKES) for IEEE 802.15.4 security is deemed to be resilient to denial-of-sleep attacks thanks to its energy-efficient design and special defenses. However, thus far, AKES’ resilience to denial-of-sleep attacks was presumably never evaluated. In this paper, we make two contributions. First, we evaluate AKES’ resilience to denial-of-sleep attacks both theoretically and empirically. We particularly consider two kinds of denial-of-sleep attacks, namely HELLO flood attacks, as well as what we introduce in this paper as “yo-yo attacks”. Our key finding is that AKES’ denial-of-sleep defenses require trade-offs between denial-of-sleep resilience and the speed at which AKES adapts to topology changes. Second, to alleviate these trade-offs, we devise and evaluate new denial-of-sleep defenses. Indeed, our newly-devised denial-of-sleep defenses turn out to significantly accelerate AKES’ reaction to topology changes, without incurring much overhead nor sacrificing on security.