“Faites de beaux rêves, monsieur," she called as she put out the light.
Switters had always loved that expression, "Make fine dreams." In contrast to the English, "Have sweet dreams," the French implied that the sleeper was not a passive spectator, a captive audience, but had some control over and must accept some responsiblity for his or her dreaming. Moreover, a "fine" dream had much wider connotations than a "sweet" one.

―Tom Robbins