The invention relates to R-hydroxynitrillyases from the family of Rosaceae that are characterized by an improved substrate tolerance and increased stability. In the active center of the R-hydroxynitrillyases either a) an alanine group is substituted by glycine, valine, leucine, isoleucine, or phenylalanine or b) a phenylalanine group is substituted by alanine, glycine valine, leucine or isoleucine, or c) a leucine group is substituted by alanine, glycine, valine, isoleucine or phenylalanine, or d) an isoleucine group is substituted by alanine, glycine, valine, leucine or phenylalanine. The invention also relates to the use of these lyases in the production of enantiomer-pure R- or S-cyanohydrines.