  The free propagator for the scalar $\lambda \phi^4$--theory is calculated
exactly up to the second derivative of a background field. Using this
propagator I compute the one--loop effective action, which then contains all
powers of the field but with at most two derivatives acting on each field. The
standard derivative expansion, which only has a finite number of derivatives in
each term, breaks down for small fields when the mass is zero, while the
expression obtained here has a well--defined expansion in $\phi$. In this way
the resummation of derivatives cures the naive IR divergence. The extension to
finite temperature is also discussed.
