A spurious timeout (STO) leads to an unnecessary go-back-N retransmission and throughput degradation, which negatively impacts the user's TCP performance. In this paper, we propose an STO detection and congestion window control algorithm based on the first acknowledgment following an RTO monitoring event for suppressing both the unnecessary retransmission and throughput degradation. This method strongly supports the enhancement of existing mobile communications systems because it does not require additional information or receiver modification.