A wind turbine generator includes a gearbox, wherein the gearbox includes a planetary gear system, wherein the planetary gear system includes a carrier assembly, wherein the carrier assembly includes a carrier supporting at least one planetary gear that is rotatably mounted through a bearing on a shaft, wherein the shaft is fixed in a bore defined by the carrier. The carrier assembly includes interlocking means to prevent angular movement of the shaft relative to the bore. This improves the robustness of the coupling between the shaft and the bore of the carrier.