A first signal field to be included in a preamble of a physical layer (PHY) data unit is generated. The first signal field includes formatting information for a second signal field to be included in the PHY data unit. The formatting information includes an indication of a number of orthogonal frequency division multiplexing (OFDM) symbols in the second signal field. The second signal field is generated according to the formatting information in the first signal field. The second signal field includes formatting information for a data portion of the PHY data unit. The data portion is generated according to the formatting information in the second signal field. The preamble is generated to include at least the first signal field and the second signal field, The PHY data unit is generated to include the preamble and the data portion.