While the literature on stakeholder engagement and that of open strategy evolved independently from each other, they both inquire over a similar empirical phenomenon: how organizational managers include stakeholders in certain organizational activities. Despite this growing interest in the phenomenon, we still know very little about how stakeholders actually make their way into strategy-making when they are not invited. To fill this research gap, our paper asks: How do stakeholders infiltrate a strategy-making process? Adopting an action-research methodology, this article explores the stakeholder engagement process of a business school that led to the co-construction of the climate strategy. We found that due to the infiltration of diverse group of stakeholders, an initially classic strategy-making process evolved into an OS process, reaching more ambitious climate goals that those initially foreseen. We contribute to the literature on stakeholder engagement, by conceptualizing the role of stakeholders in fostering organizations’ engagement activities and shaping the definition of organizational issues, and to the literature on open strategy by showing how stakeholders exercising pressures over the organization for openness in areas not originally planned, lead to more ambitious climate strategies, rather than finishing up as ephemeral events.