Abstract: Unwrapping the political discourse against immigration is key to understanding the rise of populism in Western democracies. A growing body of literature has found ample evidence that immigration pays a premium to conservative political forces that propose tighter policies. Using data on presidential elections in Spain from 2008 to 2019, we shed light on this debate by highlighting the role played by irregular migration. Some studies show that undocumented immigrants consume less and earn lower wages than documented immigrants with similar observable characteristics. In addition, since they are relegated to working in the informal sector, they cannot contribute to the welfare state with direct taxes. This suggests that undocumented migration might intensify support for right-wing politics and that the effect is independent from the one caused by the presence of documented migrants. We apply an instrumental variable strategy to deal with the non-random distribution of migrants across political districts. Our findings indicate that increasing undocumented migration increases support for the right, while increasing documented migration rises support for the left. When we consider the irruption of the far-right into electoral competitions, we find that undocumented migration redistributes votes from the left to the right, as has been observed in other countries.