A bladed rotor system for a turbomachine, comprising: a circumferential row of blades mounted on a rotor disc, each blade comprising: an airfoil extending span-wise along a radial direction from a root portion to an airfoil tip; and a shroud attached to the airfoil at a span-wise height of the airfoil, wherein in operation, shrouds of adjacent blades abut circumferentially, wherein the row of blades comprises a first set of blades and a second set of blades, the airfoils in the first and second set of blades having substantially identical cross-sectional geometry about a rotation axis, wherein 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 (H, L), whereby the natural frequency of a blade in the second set differs from the natural frequency of a blade in the first set by a predetermined amount, and wherein 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; wherein the shroud is a tip-shroud attached to the airfoil tip; wherein the shrouds in the second set of blades have a smaller mean radial thickness in relation to the shrouds in the first set of blades; and characterised in that the airfoils in the second set of blades have a correspondingly larger radial length from the root portion to the airfoil tip, in relation to the airfoils in the first set of blades, such that a sum total of the radial length of an airfoil and a radial thickness of the associated shroud at the point of attachment with the airfoil tip is constant across the first and second set of blades. a circumferential row of blades mounted on a rotor disc, each blade comprising: an airfoil extending span-wise along a radial direction from a root portion to an airfoil tip; and a shroud attached to the airfoil at a span-wise height of the airfoil, wherein in operation, shrouds of adjacent blades abut circumferentially, an airfoil extending span-wise along a radial direction from a root portion to an airfoil tip; and a shroud attached to the airfoil at a span-wise height of the airfoil, wherein the row of blades comprises a first set of blades and a second set of blades, the airfoils in the first and second set of blades having substantially identical cross-sectional geometry about a rotation axis, wherein 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 (H, L), whereby the natural frequency of a blade in the second set differs from the natural frequency of a blade in the first set by a predetermined amount, and wherein 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; wherein the shroud is a tip-shroud attached to the airfoil tip; wherein the shrouds in the second set of blades have a smaller mean radial thickness in relation to the shrouds in the first set of blades; and characterised in that the airfoils in the second set of blades have a correspondingly larger radial length from the root portion to the airfoil tip, in relation to the airfoils in the first set of blades, such that a sum total of the radial length of an airfoil and a radial thickness of the associated shroud at the point of attachment with the airfoil tip is constant across the first and second set of blades.