Light curves of GRB 130603B, indicated detections with dots and upper limits (3σ) with arrows. V-band photometry has been scaled and plotted together with the g-band. The vertical lines indicate the times when spectra were obtained. Dotted lines indicate the light curve fits to a power law temporal decay from 0.3 to 3 days after the burst. We include data from the literature (Cucchiara et al. 2013a; Tanvir et al. 2013). The dashed blue line is the expected r-band light curve of a supernova like SN 1998bw, the most common template for long GRBs after including an extinction of A_V = 0.9 magnitude. The most constraining limits indicate that any supernova contribution would be at least 100 times dimmer than SN 1998bw in the r-band, once corrected of extinction (blue dashed-dotted line).