In this work we investigate some regularization properties of the incompressible Euler equations and of the fractional Navier-Stokes equations where the dissipative term is given by (−∆) α , for a suitable power α ∈ (0, 1 2 ) (the only meaningful range for this result). Assuming that the solution u ∈ L ∞ t (C θ x ) for some θ ∈ (0, 1) we prove that u ∈ C θ t,x , the pressure p ∈ C 2θ− t,x and the kinetic energy e ∈ C 2θ 1−θ t . This result was obtained for the Euler equations in [Is13] with completely different arguments and we believe that our proof, based on a regularization and a commutator estimate, gives a simpler insight on the result.