We present a key management scheme, Assisted Mode, for improving security of LoRaWAN. LoRaWAN stores lifetime root keys in end-devices which are susceptible to physical compromise, and lacks mechanisms to update the root keys. Since security of LoRaWAN is intrinsically dependent on root keys, this practice makes LoRaWAN vulnerable to attacks on end-devices, and malpractices in their manufacturing. Due to the lifetime nature of the root keys and long lifetime of end-devices, cryptoperiods of LoRaWAN's security keys exceed recommended values. Moreover, if LoRaWAN's root keys are exposed, security of sessions which took place before the exposure are weakened. Assisted Mode addresses these problems by freeing the end-devices from management of lifetime keys, and delegating these tasks to a master device. Unlike most existing schemes, security is improved without necessitating significant changes to the protocol or incurring overhead on LoRa communications. Assisted Mode is a promising scheme for complementing LoRaWAN's key management in healthcare monitoring applications, and in other applications where the introduction of a master device is practical.