We revisit the problem of a resonant interaction between the electromagnetic extraordinary and two electrostatic waves in uniform plasmas. Starting from analysis of the kinetic equation, we eventually get the formal integral representation of the coupling coefficients describing this nonlinear phenomenon and simplify it substantially. The final expressions for the coupling coefficients are obtained in the form convenient for numerical analysis. We prove them to obey the Manley–Rowe symmetry and compare the derived formula to the one obtained within the cold-fluid model.