Few high-redshift, radio-loud quasars are known to date. The extremely luminous, radio-bright quasar, SDSS J013127.34-032100.1 was recently discovered at a redshift of z = 5.18. We observed the source with high resolution very long baseline interferometry (VLBI) at 1.7 GHz with the European VLBI Network (EVN) and found a single compact radio component. We estimated a lower limit to the brightness temperature of the detected radio component, T_B ~10¹¹ K. Additionaly, when compared to archival radio data, the source showed significant flux density variation. These two findings are indicative of the blazar nature of the source.