Our Research Highlight ‘Diamond geezers’ (Nature 437, 4; 200510.1038/437004a) described a diamond material as “harder than the real thing”. This is incorrect: the material is less compressible than diamond, as revealed through measurements of the bulk modulus. The reference for ‘Keep your options open’ ( Nature 437, 298; 2005) should have been: Cell 122, 947–956 (2005). Apologies for the errors.