Protectionist instruments such as tariffs may distort the price of traded goods. In this paper, we explore the impact of specific (per-unit) duties on the patterns of agricultural trade. Specific duties are showed to encourage countries to export products with higher prices, leading to an “Alchian Allen effect” on unit values. Their restrictive effect on trade values is smaller for developed countries as compared to developing countries. It can be explained by the quality specialization of these countries, but also by the low level of quality differentiation of their exports. Our results highlight the discriminating nature of specific duties for low-income countries.