A gas turbine rotor blade including a root portion, a platform and an airfoil portion arranged along a span direction 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 with a minor component of extension in span direction, 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 and a component of extension perpendicular to the span direction 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 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 with a minor component of extension in span direction, 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 and a component of extension perpendicular to the span direction 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 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 defined from an upstream end of the axial groove to a junction of the further groove and the axial groove.