Rosetting, the formation of red blood cell aggregates, is a life-threatening condition in Malaria tropica and not yet fully understood. We study rosette stability using a set of microfluidic stenotic channels, with varied narrowing angle and erythrocytes of blood groups 0 and A. We find reduced ability of a rosette to pass a stenosis without disruption, the longer the tapered part of the constriction and the narrower the stenosis is. In general, this ability increases with rosette size and is 5%-15% higher in blood group A. The experimental results are substantiated by equivalent experiments using lectin-induced red blood cell aggregates, a simulation of the underlying protein binding kinetics, and lattice-Boltzmann-finite-element simulations of red blood cell aggregates.