During operation, an interface circuit in an electronic device may receive, from a second electronic device (such as an access point in a WLAN), an uplink trigger frame that may specify an access category. In response to the uplink trigger frame, the electronic device may first include data associated with the specified access category in one or more frames, and then may transmit the one or more frames to the second electronic device. Moreover, when all the data associated with the specified access category has been transmitted or when there is no data associated with the specified access category, and when there is leftover time in an allocation associated with the uplink trigger frame, the interface circuit may transmit the one or more frames to the second electronic device with additional data associated with another access category that is different from the specified access category.