Stars with anomalous extinction sightlines in the λ_max-K plane. Blue shows stars with anomalous sightlines observed with FORS2 (circles), CAHA (right pointing triangles), AFOSC (squared), and HPOL (left-pointing triangles). The solid blue line represents the linear best fit to the sample, and its 1σ deviation (dotted). The dashed black line traces the Whittet et al. (1992) relation and its 3σ uncertainty(dotted). For comparison, a sample of SNe Ia from Patat et al. (2015) and Zelaya et al. (2017; see Appendix B) are marked with stars and red contours, which indicate the 10 and 20 σ confidence levels for SN 2008fp and SN 2014J.