We present measurements of the K I λ 7699 line from spectra of 19 late-type members of the αPersei cluster obtained with the Intermediate Dispersion Spectrograph at the Isaac Newton Telescope. These stars span a narrow range of Teff, from 5091 K to 4771 K, and a wide range of v sin i values (9 km s-1-170 km s-1). For a given star, we find empirically that larger rotational broadening apparently increases the equivalent width of K I λ 7699 linearly for v sin i values from 15 km s-1 to 75 km s-1. This correlation breaks down for v sin i > 75 km s-1. After correction for this effect, we show that the potassium line equivalent widths do not really correlate with v sin i. Based on observations made with the Isaac Newton Telescope, operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.