  An upper bound on the parameter that provides a generalized uncertainty
principle (GUP) is obtained from the black hole shadow. With the aid of a
recent constraint between regular black holes and the GUP parameter, it is
indicated a relation between this parameter and the deviation from circularity
of the black hole shadow. In the case of the recent announcement of the M87*
results from the Event Horizon Telescope collaboration, a deviation from
circularity $\lesssim 10\%$ imposes a GUP parameter $\beta_0 <10^{90}$.

General Relativity and Quantum Cosmology;High Energy Physics - Theory