The development of grammatical markers has been described from several theoretical perspectives over the last decade: Grammaticalization Theory (Hopper & Traugott 2003, Heine, Claudi & Hünnemeyer (1991), the Minimalist Program (Roberts & Roussou 2003, van Gelderen 2004), and Lexical-Functional Grammar (Vincent 2001), see also the overview in (Börjars & Vincent 2010). It has recently been addressed in Construction Grammar, where it is argued that a shift towards a constructional perspective on change may yield new insights into the workings of grammaticalization (Bergs & Diewald 2008, Hoffmann & Trousdale 2013, Traugott & Trousdale 2013). This paper should be taken as a contribution to a constructional view on grammaticalization. It is about the rise of the concessive subordinator fast(än) in the history of Swedish occurring in a construction or clause type called universal concessive conditional (Haspelmath & Köning 1998), in Swedish generaliserande bisats (SAG 1999). The Swedish fast, etymologically (and still productively) as an adjective in the meaning ‘steady’, ‘robust’ is used as an intensifier, ‘very’, ‘much’, in early Modern Swedish, eventually established as a concessive marker ‘even if’, ‘although’ in the 18th century. The conventionalization of a concessive inference is highly interesting and may be traced back to specific constructions in the 16th and 17th centuries. On the basis of an extensive corpus study, I analyze the critical contexts and discuss the development as constructional change rather than lexical change, arguing that a remapping between form and function takes place in concessive conditional constructions due to processes of inferencing and mismatch.