This paper studies the impact of green fiscal rules – designed to protect climate-related spending –on debt dynamics. Simulations of green rules that exempt green spending from the rule limits for an emergingmarket economy illustrate that they can lead to unsustainable debt dynamics when the net zero emissions goal is pursued mostly using spending-based instruments (e.g., investment and subsidies). Or the rule would need to implicitly assume a large fiscal adjustment in the non-green budget,