Modeling adaptivity is a challenging task for two reasons: 1) adaptation is usually strongly interwoven with the general functionality of the web application, separation of concerns is hard to achieve, and 2) adaptation rules may be conflicting, i.e., changing and revoking the effect of each other. We propose to use our aspect-oriented extension of UML state machines, High-level Aspects (HiLA), to model adaptation rules of web applications. With HiLA, adaptation rules can be modeled separately from the general functionalities. We also provide an automatic technique for checking the consistency of the aspects (i.e., the adaptation rules). Therefore, HiLA provides valuable help for modularly modeling adaptive web applications and keeping the adaptation rules consistent.