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Intracellular transport by molecular motors proceeds in two steps: long-range transport along microtubules and local delivery via actin filaments. A recent in vitro experiment has revealed that the actin-based motor myosin V can diffuse along microtubules and can enhance the processivity of cargos pulled by the microtubule-based motor kinesin-1 (Ali MY et al., Proc. Natl. Acad. Sci. USA, 105 (2008) 4691). Here we present a stochastic model for cargo transport by a directional motor (kinesin) and a diffusing motor (myosin). By using a subset of the experimental data of Ali et al. to adjust our model parameters, we are able to describe all experimental results. In our model, the myosins do not influence kinesin's motion and only act as tethers which allow the kinesin to rebind. Furthermore we find that the run length of the cargo increases exponentially with the number of myosins.