The number of applications based on Global Navigation Satellite System (GNSS) technology is constantly increasing; consequently, the requirements related to signal quality are becoming more and more important. This paper exploits results of the decision theory, aiming at investigating the performance of the goodness of fit test when applied to interference detection in GNSS receivers. It proposes two versions of a signal quality monitoring algorithm: one working exclusively precorrelation, the other providing postcorrelation information as well.