Massive stars with confirmed magnetic field detections in the Hertzsprung-Russell diagram (Briquet et al. 2013; Petit et al. 2013; Alecian et al. 2014; Neiner et al. 2014; Fossati et al. 2014, 2015a; Sikora et al. 2015; Castro et al. 2015, grey circles), and CPD −57° 3509 (black dot). Error bars are 1σ uncertainties. Evolutionary tracks of Brott et al. (2011) for initial rotational velocity of ~300 km s^-1 are shown (full lines), labelled by initial stellar mass. The magnetic star in the Trifid nebula and HD 345439 (Hubrig et al. 2014, 2015b) are not included here because of difficulties in establishing their properties.