Provided is a circuit for preventing local area network packets shorter than a predetermined bit length from being received by a local area network coprocessor. Serial data which would otherwise be received by the coprocessor is delayed by a data-shift register of predetermined bit length. Simultaneously, a carrier-sense-signal, which alerts the coprocessor that serial data is ready to be received, is modified by a carrier-sense-signal regeneration circuit. If the carrier-sense-signal is detected true by the regeneration circuit for a number of clock cycles equal to the number of bits in the data-shift register, then the carrier-sense-signal is delivered to the coprocessor and the data in the data-shift register is received by the coprocessor. Once the carrier-sense signal goes false, the regeneration circuit continues to deliver the carrier-sense-signal until the data-shift register empties.