Particle production from vacuum fluctuations during inflation is briefly revisited. The moduli problem occurringwith light particles produced at the end of inflation is addressed, namely the fact that some results arein disagreement with nucleosynthesis constrains. A universal solution to this problem is found which leads toreasonable reheating temperatures in all cases. It invokes the assumption that, immediately after inflation, themoduli evolve like non-relativistic matter. The assumption is justified in the context of massive chaotic inflationwere, at the end of inflation, the universe evolves as if it was matter-dominated.