  We present a model based on the idea that Planck-scale effects may produce a
small explicit breaking of global symmetries. The model contains a new complex
scalar field $\Psi$, charged under a certain global U(1) symmetry, interacting
with a new real scalar field $\chi$, neutral under U(1). For exponentially
small breaking, the model accounts for both {\em early} and {\em late} periods
of acceleration of the universe.
