Shrinkage requires planners to move away from growth-oriented planning towards an adaptive approach. It is puzzling that even after decades of shrinkage, planners can still be stuck with a growth mindset that results in wasted resources and little gain. Existing research has done little to comprehend why planning policy adapts so slowly to shrinkage. The article revolves around the question: What shapes planning policy in shrinking regions? This question is addressed through a case study conducted in the Spanish region of Asturias. The study makes a first analysis of how ideas, interests and institutions influence policy change in shrinking regions. It finds that institutional structures and local interests can be serious obstacles to the adoption of adaptive planning approaches.