Let f (z) be a holomorphic normalized Hecke-eigen cusp form of weight kappa for SL2 (Z) with Fourier coefficients lambda(f) (n). In this paper, we estimate the sum of lambda(f) (n) at primes twisted with exponential functions e(alpha P-theta) for 0 < theta < 1. New upper bounds are proved for fixed alpha. Similar results are also given for the analogous situation of non-holomorphic forms. (C) 2019 Elsevier Inc. All rights reserved.