The effects of corporate governance on optimal capital structure choices have been well documented, though without offering empirical evidence about the impact of corporate governance quality on the adjustment speed toward an optimal capital structure. This study simultaneously considers two effects of debt originating from agency theory—the takeover defense and the disciplinary effects of debt—on the speed of adjustment to the optimal capital structure. Corporate governance has a distinct effect on the speed of capital structure adjustment: weak governance firms that are underlevered tend to adjust slowly to the optimal capital structure, because the costs of the disciplinary role of debt outweigh the benefits of using debt as a takeover defense tool. Although overlevered weak governance firms also adjust slowly, they do so because they are reluctant to decrease their leverage toward the target level to deter potential raiders, especially if they face a serious takeover threat. Therefore, this study finds that both overlevered and underlevered firms with weak governance adjust slowly toward their target debt levels, though with different motivations.