How do movements that emerge not to directly challenge established institutions, but to defend them, construct ideational frames? What balance do they strike between identifying the problem, apportioning blame and articulating an alternative? Whilst recent scholarship places great emphasis on movements as ‘meaning makers’ and distinguishes between ‘diagnostic’ and ‘prognostic’ frames, the social movement literature has had little to say regarding the interaction between these two types of frame. From the perspective of the anti-Brexit campaign in the UK, we address the interplay between prognostic and diagnostic frames. Our comparative analysis of campaign materials and interview data reveals that the movement faced key challenges in terms of formulating: a) a diagnostic frame that struck the right balance between problematizing the current political situation whilst supporting the established order; and b) a prognostic frame that extended beyond a defence of the status quo that has been the subject of growing public dissatisfaction. Yet diagnostic and prognostic frames should also be considered in conjunction: in the absence of a more precise diagnosis of underlying problems feeding Euroscepticism, it is hardly surprising that the prognostic frames of the anti-Brexit movement remained underdeveloped.