The SBAS (Satellite-Based Augmentation System) is the standard system which augments GNSS using geostationary satellites. The SBAS transmits the clock-ephemeris covariance matrix as Message Type 28 to give users capability to compute ranging accuracy at any user location, but this message was not defined in the initial version of the SBAS standards. In order to ensure backward compatibility with the initial standards, the current version of the SBAS standards defines receiver operation without Message Type 28. This means receivers may operate even before the reception of Message Type 28 and cause loss of integrity with integrity parameters generated subject to the existence of Message Type 28. The author has investigated and observed such a possibility for MSAS, just about 0.14% of time, thus here reports the situation with a mitigation measure.