A method for buffering media data in a buffer where the media data is included in data transmission units which have been ordered in a transmission order which is at least partly different from a decoding order of the media data in the data transmission units. The decoding order is indicated with a quantitative indicator for at least part of the transmission units. In the method a parameter is defined for a relation of the quantitative indicators of transmission units. The relation of transmission units in the buffer is checked against the parameter. The result of the checking is indicative of at least one transmission unit in the buffer preceding, in decoding order, any transmission unit in a sequence of transmission units not having been buffered in the buffer before the checking.