Miniaturized light-level geolocators are becoming increasingly popular devices for the study of avian migration. However, the effects of these devices on birds’ flight behaviour and hence fitness components are poorly known. We investigated the effect of miniaturized geolocators on flight performance of the Barn Swallow (Hirundo rustica), which may be especially susceptible to geolocator deployment because it is a small (20 g), aerially insectivorous, long-distance migratory species. We tested whether miniaturized geolocators (3.5% of body mass) affect short-term flight performance traits of breeding males by comparing flight manoeuvrability, velocity and acceleration of geolocator-equipped vs. control (handled only) birds in flight tunnels. We used a robust experimental design where the within-individual change in flight performance was compared between geolocator-equipped birds (after allowing for a period of acclimation) and control birds (that were also tested twice). We found no statistically significant evidence that short-term flight performance traits were affected by geolocator deployment. We discuss the implications of our findings for the deployment of geolocators in studies of migratory behaviour of small birds.