The ratio of the reaction rates of the competing channels O-17(alpha,gamma)Ne-21 and O-17(alpha,n)Ne-20 determines the efficiency of O-16 as a neutron poison in the s process in low metallicity rotating stars. It has a large impact on the element production, either producing elements to the mass range of A=90 in case of a significant poisoning effect or extending the mass range up to the region of A=150 if the gamma channel is of negligible strength. We present an improved study of the reaction O-17(alpha, n)Ne-20, including an independent measurement of the O-17(alpha, n(1))Ne-20 channel. A simultaneous R-Matrix fit to both the n(0) and the n(1) channels has been performed. New reaction rates, including recent data on the O-17(alpha,gamma)Ne-21 reaction, have been calculated and used as input for stellar network calculations and their impact on the s process in rotating massive stars is discussed.