Error flag screening unit (130; 230; 330) for a subscriber station (10; 20; 30) of a serial bus system, in which, in a first communication phase for transmitting a message (45; 46) to a bus of the bus system, it is negotiated between the subscriber stations (20, 30) of the bus system which of the subscriber stations (20, 30) at least temporarily has exclusive, collision-free access to the bus of the bus system in a subsequent second communication phase, wherein the second communication phase is a data phase in which useful data of the message (45; 46) are transmitted on the bus, and wherein the error flag screening unit (130; 230; 330) has a data-phase detection block for detecting the data phase of the message serially transmitted on the bus, and a transmitter detection block for detecting whether or not the subscriber station (10; 20; 30) is currently the transmitter of the message (45, 46) serially transmitted on the bus, a screening decision block for generating a signal (S_D) in response to a detection result (NG_DP) of the data-phase detection block and a detection result (TX_ND) of the transmitter detection block, wherein the screening decision block is configured to set the signal (S_D), during transmission of the data phase of a message on the bus of the bus system for which message the subscriber station (10; 20; 30) is not currently the transmitter, to a first predetermined value which indicates that a transmission signal, which was created by the subscriber station (10; 20; 30) during the data phase due to the identification of a reception error in the message received from the bus, is not to be transmitted to the bus during the data phase, and to otherwise set the signal (S_D) to a second predetermined value, and a transmission-signal selection block for blocking the transmission signal, which was created by the subscriber station (10; 20; 30) during the data phase due to the identification of the reception error in the message received from the bus and is to indicate the reception error in the message received from the bus by using an error flag on the bus, if the signal (S_D) generated by the screening decision block is set to the first predetermined value, with the result that the error flag is not transmitted to the bus, and for not blocking the transmission signal if the signal (S_D) generated by the screening decision block is set to the second predetermined value. a data-phase detection block for detecting the data phase of the message serially transmitted on the bus, and a transmitter detection block for detecting whether or not the subscriber station (10; 20; 30) is currently the transmitter of the message (45, 46) serially transmitted on the bus, a screening decision block for generating a signal (S_D) in response to a detection result (NG_DP) of the data-phase detection block and a detection result (TX_ND) of the transmitter detection block, wherein the screening decision block is configured to set the signal (S_D), during transmission of the data phase of a message on the bus of the bus system for which message the subscriber station (10; 20; 30) is not currently the transmitter, to a first predetermined value which indicates that a transmission signal, which was created by the subscriber station (10; 20; 30) during the data phase due to the identification of a reception error in the message received from the bus, is not to be transmitted to the bus during the data phase, and to otherwise set the signal (S_D) to a second predetermined value, and a transmission-signal selection block for blocking the transmission signal, which was created by the subscriber station (10; 20; 30) during the data phase due to the identification of the reception error in the message received from the bus and is to indicate the reception error in the message received from the bus by using an error flag on the bus, if the signal (S_D) generated by the screening decision block is set to the first predetermined value, with the result that the error flag is not transmitted to the bus, and for not blocking the transmission signal if the signal (S_D) generated by the screening decision block is set to the second predetermined value.