We report a complete analytical expression for the one-loop correction to the ac conductivity $sigma(omega)$ of a disordered two-dimensional electron system in the diffusive regime. The obtained expression includes the weak localization and Altshuler-Aronov corrections as well as the corrections due to superconducting fluctuations above superconducting transition temperature. The derived expression has no $1/(iomega)$ divergency in the static limit, $omegato 0$, in agreement with general expectations for the normal state conductivity of a disordered electron system.