A method and an arrangement in a radio network node for adapting transmission power of resource elements for demodulation reference signals, referred to as “reference elements” are provided. The radio network node is configured for multiple-input multiple-output transmission, referred to as “MIMO transmission”, to a user equipment. The MIMO transmission comprises at least three layers. Two consecutive subcarriers of a resource block carry at least three reference elements. A first subcarrier of the resource block carries data elements. The radio network node adapts transmission power of said at least three reference elements such that an average transmission power, over said two consecutive subcarriers, of said at least three reference elements is equal to a transmission power, for the first subcarrier, of the data elements for said at least three layers. The radio network node uses the adapted transmission power to transmit, to the user equipment, said at least three reference elements.