Aims. We analyzed the C I lines associated with the damped Lyα system observed at z_abs = 1.15 in the spectrum of HE 0515-4414 to derive the ¹²C/¹³C ratio. Methods. The spectrum was obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). Results. The obtained lower limit ¹²C/¹³C > 80 (2σ C.L.) shows for the first time that the abundance of ¹³C in the extragalactic intervening clouds is very low. This rules out a significant contribution from intermediate-mass stars to the chemical evolution of matter sampled by this line of sight. The estimated low amount of ¹³C is in agreement with low abundances of nitrogen observed in damped Lyα systems - the element produced in the same nuclear cycles and from about the same stars as ¹³C.