Hyperfine-structure parameters and isotope shift of the 9/2- isomeric state in Au187 relative to Au197 for the 267.6-nm atomic transition have been measured for the first time using the in-source resonance-ionization spectroscopy technique. The magnetic dipole moment and change in the mean-square charge radius for this 9/2- isomer have been deduced. The observed large isomer shift relative to the 1/2+ ground state in Au187 confirms the occurrence of the shape coexistence in Au187 proposed earlier from the analysis of the nuclear spectroscopic data and particle plus triaxial rotor calculations. The analysis of the magnetic moment supports the previously proposed 9/2-, 1/2-[541] assignment at moderate prolate deformation for Aum187.