After almost 25 years of uninterrupted work, the RT4 radio telescope - the most important instrument at the Astronomical Observatory of the Nicolaus Copernicus University in Piwnice near Toruń and the largest antenna of this type in Poland - has undergone renovation works. Numerous corrosion centers were removed from the antenna structure, then the entire instrument was re-painted, and particular attention was paid to the appropriate protection of the reflecting surfaces of the main and secondary mirrors.