The third generation partnership project (3GPP) has issued specifications for the autonomous assignment of radio resources by vehicles on the sidelink of the cellular-vehicle-to-everything (C-V2X) technology. It is based on a sensing mechanism for resource selection and a semi-persistent scheduling for resource reservation to periodic safety messages. Imperfect sensing due to hidden terminals and to half-duplex on board transceivers may result in the selection of interfered resources for successive message transmissions. As a consequence of the lost packets, involved vehicles may become blind to the presence of other vehicles in their vicinity even for many seconds, with threats to the road safety. In this paper, we define these events as wireless blind spots (WBSs) and characterize their probability to occur. We propose an enhancement to the autonomous mode in order to reduce the WBS duration and demonstrate the benefits of the proposal against the legacy mode, both analytically in a simplified scenario and through simulations in a highway environment.