This contribution aims at analyzing one case of resistance to interference, with the ultimate goal of contributing to a predictive theory of the conditions on contact-induced language change. This paper explores the possibility that interference is necessarily the result of structural reanalysis of strings of E-language already weakly generated in the targeted grammar. We construe the Resistance Principle as a formalization of Weinreich’s (1953) observation that interference can be blocked by structural incompatibility between the Source and Target language; this is done by formulating it in terms of set-theoretic relations among the strings generated and used to trigger parameter values.