  Recently it was shown that if the matter congruence of a general relativistic
perfect fluid flow in an almost FLRW universe is shear-free, then it must be
either expansion or rotation-free. Here we generalize this result for a general
f(R) theory of gravity and show there exist scenarios where this result can be
avoided. This suggests that there are situations where linearized forth-order
gravity shares properties with Newtonian theory not valid in General
Relativity.
