The recent IR scholarship has been increasingly occupied with research on the complex processes of norm dynamics. The object of inquiry would therefore be not only the emergence and diffusion of norms but also their post-inception evolution, strengthening, weakening, erosion and possibly collapse. While the majority of scholars have focused predominantly on the role of norm entrepreneurs as dominant actors in the process, the present paper aims to explore the logic of action as well as impact of practices of norm-defying states. In two case studies, the author examines the norm-eroding conduct of North Korea and Pakistan and its impact on dynamics of three norms which are considered to be critical for functioning of Nuclear Non-proliferation Treaty (NPT) regime: nuclear non-proliferation, non-testing and non-use. The preliminary findings highlight the relevance of interaction capacity of particular defiant states, the coercive potential of their conduct and the critical importance of inter-norm dynamics. As such, the study contributes to our deeper understanding of the role of defiant states in the development of international norms and regimes and suggests policy implications for NPT regime in particular.