  We derive an alternative to the Wetterich-Morris-Ellwanger equation by means
of the two-particle irreducible (2PI) effective action, exploiting the method
of external sources due to Garbrecht and Millington. The latter allows the
two-point source of the 2PI effective action to be associated consistently with
the regulator of the renormalization group flow. We show that this procedure
leads to a flow equation that differs from that obtained in the standard
approach based on the average one-particle irreducible effective action.
