H I spectra of AGC 226178 from ALFALFA, FAST, and the VLA. The grey curve is the public ALFALFA spectrum from Haynes et al. (2018); the blue curve is for the natural-weighted cube of the VLA; the black curve is the FAST spectrum extracted using a 4.2′×3.5′ elliptical aperture centred on AGC 226178; the dashed line represents the Gaussian fit for the main component, whereas the dash-dotted line corresponds to a fit of a Gaussian to the second part of the system (i.e. the low-velocity extension in the position velocity diagram shown in Fig. 1). The red dashed curve represents the FAST spectrum extracted from a beam-sized aperture centred on the nearby galaxy NGVS 3543.