  We report on measurements of the in-plane magnetic penetration depth
\lambda_{ab} in the infinite-layer electron-doped high-temperature cuprate
superconductor Sr_0.9La_0.1CuO_2 by means of muon-spin rotation. The observed
temperature and magnetic field dependences of \lambda_{ab} are consistent with
the presence of a substantial s-wave component in the superconducting order
parameter in good agreement with the results of tunneling, specific heat, and
small-angle neutron scattering experiments.
