Method and apparatus for conveying precoding information in a control message (M) from a first node (400) to a second node (402), with information on properties of an associated wireless data transmission (D) between the first and second nodes employing spatial multiplexing and precoding for the data transmission. The first node determines precoding parameters (P) for signal transmission to the receiving node, optionally based on feedback reports (F) from the receiving node. The first node encodes control information bits in precoding information fields of the control message by means of values in TBS fields of the control message, such that the TBS field values determine the interpretation of the bits in the precoding information field(s). The control message (M) is then sent to the second node.