This paper examines the origins of amendatory vetoes in Latin America and shows why presidents' ability to present a redrafted bill after congressional passage gives them considerable power to affect legislation. The paper begins with a historical account that illustrates the workings of amendatory observations in nineteenth-century Latin America—the passage of the Electoral Law of 1874in Chile. Next, it specifies the degree to which different constitutional procedures allow presidents to redraft legislation and shows why the power to introduce amendatory observations provides greater discretion than the power of the better-known block veto, regardless of override thresholds. Lastly, the paper traces the origins of amendatory observations back to the first wave of constitution writing that followed the wars of independence. Our findings challenge prior classifications of veto powers in Latin America and highlight the positive agenda-setting power afforded to the president at the last stage of the lawmaking process.