A gas turbine rotor blade including a root portion , a platform and an airfoil portion arranged along a span direction (S) of the rotor blade with the platform being located between the root portion and the airfoil portion , the platform comprising: - an upstream side , - a downstream side , - side faces which extend from the upstream side to the downstream side , - an axial groove in each side face of the platform , which axial groove extends substantially perpendicular to the span direction (S) with a minor component of extension in span direction (S), and - a radial groove in each side face of the platform , which radial groove extends towards the axial groove with a component of extension in span direction (S) and a component of extension perpendicular to the span direction (S) and where the radial groove has a first end that shows away from the axial groove and a second end that shows towards the axial groove and where the second end is located at a distance from the axial groove so that a groove free section is formed between the second end of the radial groove and the axial groove , characterised in that : - a further groove is present in each side face of the platform , which further groove is open towards the axial groove and towards the upstream side of the platform and which further groove is inclined away from the airfoil portion , as seen from the downstream side towards the upstream side , - the axial groove and the radial groove are arranged to overlap in the axial direction, - the overlap in the axial direction is at least the length (L) defined from an upstream end of the axial groove to a junction of the further groove and the axial groove . - an upstream side , - a downstream side , - side faces which extend from the upstream side to the downstream side , - an axial groove in each side face of the platform , which axial groove extends substantially perpendicular to the span direction (S) with a minor component of extension in span direction (S), and - a radial groove in each side face of the platform , which radial groove extends towards the axial groove with a component of extension in span direction (S) and a component of extension perpendicular to the span direction (S) and where the radial groove has a first end that shows away from the axial groove and a second end that shows towards the axial groove and where the second end is located at a distance from the axial groove so that a groove free section is formed between the second end of the radial groove and the axial groove , characterised in that : - a further groove is present in each side face of the platform , which further groove is open towards the axial groove and towards the upstream side of the platform and which further groove is inclined away from the airfoil portion , as seen from the downstream side towards the upstream side , - the axial groove and the radial groove are arranged to overlap in the axial direction, - the overlap in the axial direction is at least the length (L) defined from an upstream end of the axial groove to a junction of the further groove and the axial groove . - a further groove is present in each side face of the platform , which further groove is open towards the axial groove and towards the upstream side of the platform and which further groove is inclined away from the airfoil portion , as seen from the downstream side towards the upstream side , - the axial groove and the radial groove are arranged to overlap in the axial direction, - the overlap in the axial direction is at least the length (L) defined from an upstream end of the axial groove to a junction of the further groove and the axial groove . <EOS>