Recently, the interest in the innovation of digital services based on open public information (i.e. open data) has increased dramatically. Innovation contests, such as idea competitions and digital innovation contests, have become popular instruments to accelerate the development of new service ideas and prototypes. However, only a few of the service prototypes developed at innovation contests become viable digital services. In order to strengthen the role of innovation contests as innovation instruments, we propose a framework of innovation barriers to open innovation of digital services. The framework has been designed using a systematic research approach including a literature review of existing barriers, an online survey with participants before an innovation contest, and systematic follow-up interviews with teams participating in the contest. The framework consists of 18 innovation barriers and is intended to be used when organizing innovation contests. It supports the process after the contest when prototypes are transformed into viable digital services. For future research, we suggest the framework to be validated in a longitudinal study involving additional cases. Furthermore, we suggest using the framework as a starting point for constructing guidelines that can help in designing innovation contests.