Using path-integral Monte Carlo simulations, we compute the ideal shear strength (ISS) on the basal plane of hcp He4. The failure mode upon reaching the ISS limit is characterized by the homogeneous nucleation of a stacking fault and it is found to be anisotropic, consistent with Schmid's law of resolved shear stress. Comparing the ISS of hcp He4 to a large set of classical crystals shows that it closely fits the approximately universal modified Frenkel model of ideal strength. 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