Complementors are the cornerstone of innovation and a vital part for every platform ecosystem. Nevertheless, their perspective is commonly neglected in academic research. By drawing on external resources, they develop complementary products, use distribution channels and benefit from the development of the platform and the surrounding ecosystem. Their accelerating dependence on platform owners, however, has not only created new business opportunities but also introduced essential new risks. These co-innovation risks are especially accelerated by the dominant position of the platform owner and the related uncertainty of the transaction environment. Hence, we apply a quantitative survey among 42 complementors of five leading cloud platforms to explore the drivers of such risk and the role of platform specificity, governance as well as app architecture in such settings. We thus provide valuable insights for both practice as well as theory on platform ecosystems.