Mate-copying is a form of social learning in which witnessing sexual interactions between conspecifics biases an observer individuals’ future mate-choice. Mate-copying exists in many vertebrates, as well as in Drosophila melanogaster. Here, we show that female fruit flies can copy the choice for mutant males [curly wings (Cy) mutants versus wild types (WT)] despite the fact that mating with Cy males induce a significant fitness cost for the observer female. When facing WT and Cy males, naive observer females of both phenotypes naturally prefer WT males. In a mate-copying experiment, naive observer Cy or WT females saw a demonstrator female copulating with either a Cy or a WT male aside a lonely male of the opposite phenotype. In the subsequent mate-choice test, Cy and WT observer female did not change their already high natural preference for WT males after witnessing a WT male copulating during the demonstration. Contrastingly, Cy and WT female increased their preference for the naturally non-preferred Cy males after witnessing a Cy male copulating, showing that mate-copying also exists for costly variants in invertebrates. Furthermore, mate-copying efficiency did not differ when using neutral artificial variants (colouring, Dagaeff et al. 2016, Animal Behaviour) versus phenotypic variants (this study), suggesting that these two types of experiments are equivalently suitable to study mate-copying. We finally discuss how mate-copying can participate to the maintenance of costly traits in a population.