Flux spectrum and the ISP-corrected polarisation degree P, Stokes Q and U parameters, and the polarisation angle θ for SN 2017gci at +3.3 d (left) and +29.0 d (right). The polarimetry data are binned to 25 Å in rest frame for visual clarity, but the flux spectra are shown at the natural binning of the spectrograph (∼3.3 Å). The most notable line features (vertical lines) and telluric bands (grey regions) are highlighted. At +3.3 d, the polarisation degree increases towards the red, while at +29.0 d it is found at a consistently low value.