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 (H) of blades and a second set (L) of blades , the airfoils in the first (H) and second (L) set of blades having substantially identical cross-sectional geometry about a rotation axis , wherein the blades of the second set (L) are distinguished from the blades of the first set (H) 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 (L) differs from the natural frequency of a blade in the first set (H) by a predetermined amount, and wherein blades of the first set (H) and the second set (L) 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 (L) of blades have a smaller mean radial thickness in relation to the shrouds in the first set (H) of blades ; and characterised in that the airfoils in the second set (L) 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 (H) 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 (H) and second (L) 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 (H) of blades and a second set (L) of blades , the airfoils in the first (H) and second (L) set of blades having substantially identical cross-sectional geometry about a rotation axis , wherein the blades of the second set (L) are distinguished from the blades of the first set (H) 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 (L) differs from the natural frequency of a blade in the first set (H) by a predetermined amount, and wherein blades of the first set (H) and the second set (L) 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 (L) of blades have a smaller mean radial thickness in relation to the shrouds in the first set (H) of blades ; and characterised in that the airfoils in the second set (L) 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 (H) 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 (H) and second (L) set of blades . <EOS>