Each year, billions of dollars of public funds are expended to purchase conservation easements on farmland. One unintended impact of these programs is that they may bring non-cropland into crop production. Such a slippage effect can be caused by increased output prices and by substitution effects. This article shows that for each one hundred acres of cropland retired under the Conservation Reserve Program (CRP) in the central United States, twenty acres of non-cropland were converted to cropland, offsetting 9 and 14% of CRP water and wind erosion reduction benefits, respectively. Implications of these results for the design of conservation programs are discussed.