We consider the initial-value problem for the ``good Boussinesq equation on the line. Using inverse scattering techniques, the solution can be expressed in terms of the solution of a $3 times 3$-matrix Riemann-Hilbert problem. We establish formulas for the long-time asymptotics of the solution by performing a Deift-Zhou steepest descent analysis of a regularized version of this Riemann-Hilbert problem.