A bladed rotor system includes a circumferential row of blades mounted on a rotor disc. Each blade includes an airfoil and a shroud attached to the airfoil at a span-wise height of the airfoil. The row of blades includes a first set of blades and a second set of blades. The airfoils in the first and second set of blades have substantially identical cross-sectional geometry about a rotation axis. The blades of the second set are distinguished from the blades of the first set by a geometry of the shroud that is unique to the respective set, whereby the natural frequency of a blades in the first and second sets differ by a predetermined amount. Blades of the first set and the second set alternate in a periodic fashion in said circumferential row, to provide a frequency mistuning to stabilize flutter of the blades.