[en] The internal strain parameter of diamond has been found from the uniaxial-stress-dependence of the integrated intensity of the 'forbidden' 006 reflection. Synchrotron radiation from the storage ring DORIS-HASYLAB was conditioned by a gold mirror to provide the 006 and 008 reflections from the sample. Integrated intensities were recorded using an energy-dispersive method. The value found is anti A=-0.031±0.005 and corresponds to a bond-bending parameter ζ=0.125±0.020. This value is in accord with two recent theoretical values based on a bond-charge model and on an ab initio pseudopotential calculation. (orig.)