This paper explores the importance of acknowledging speakers' attitudes in lexical purification by focusing on Valencian, a dialect of Catalan spoken in the Autonomous Community of Valencia, eastern Spain. The Valencian vernacular is heavily Castilianized at the lexical level, despite more than twenty years of planning aimed at raising the status of Valencian and purging this variety of Spanish borrowings. Throughout this paper, it is argued that planners who wish to widen the current scope of the lexical de-Castilianization of Valencian should first change speakers' attitudes towards the non-Castilian replacements. Positive attitudes towards these lexical items are expected to strongly correlate with linguistic behavior, i.e., with the use of these lexical replacements. Finally, the paper advances an attitude-changing construct that local planners could follow should they decide to intensify the lexical de-Castilianization of Valencian.