Abstract. A generic feature of inflationary models in supergravity/string constructions is vacuum misalignment for the moduli fields. The associated production of moduli particles leads to an epoch in the post-inflationary history in which the energy density is dominated by cold moduli particles. This modification of the post-inflationary history implies that the preferred range for the number of e-foldings between horizon exit of the modes relevant for CMB observations and the end of inflation $(N_k)$ depends on moduli masses. This in turn implies that the precision CMB observables $n_s$ and $r$ are sensitive to moduli masses. We analyse this sensitivity for some representative models of inflation and find the effect to be very relevant for confronting inflationary models with observations.