We study the effects of minimum mandatory sentences when judges are at least minimally averse to error and/or follow some "penalty should fit the crime" heuristic. We apply our analysis to the 2007 reform of the French Penal Code. We show that the introduction of minimum mandatory sentences in this context may backfire inducing more crime in the long run. Judges may prefer to acquit a criminal than convicting him to a sentence reputed too high.