In this paper, I discuss six patterns of case mismatches in free relatives that arise in German. Four of the six have been accounted for in Bergsma (submitted), using grafting (Van Riemsdijk 2006) and the case hierarchy in nanosyntax (Caha 2009). I show that the (un)grammaticality of free relatives with case mismatches involving prepositions follows directly from this analysis. That is, if the embedded clause requires a less complex case than the main clause, additional merged features are spelled out by a separate lexical entry, and an override the spellout of the relative pronoun is avoided.