This article discusses the syntax–prosody interface, drawing on evidence from Stockholm Swedish. It is shown that a Swedish main clause containing an embedded clause has three prosodic correlates, two of which are non-isomorphic to the syntactic bracketing. However, two coordinated clauses have only one – isomorphic – prosodic correlate. Optimality-theoretic constraints (Prince & Smolensky 1993) are used to derive this variation. A new markedness constraint, EqualSisters, is argued to be responsible for a preference for flat prosodic structures. This constraint requires that sister nodes in prosodic structure belong to the same prosodic category, and therefore sometimes conflicts with match constraints, which call for syntax–prosody correspondence (Selkirk 2009, 2011). When high-ranked, EqualSisters forces syntax–prosody non-isomorphism if the input syntactic structure contains embedding, whereas full isomorphism is predicted in coordinated structures. The previously suggested markedness constraints Non-recursivity and Exhaustivity (Selkirk 1996) cannot replace EqualSisters, and in the present account are rendered redundant.