On May 8, 2024, the sunspot region AR13664 triggered a sequence of rapid Coronal Mass Ejections (CMEs), which proved to be geoeffective. A total of five CMEs, which caught up with one another on their way to Earth and thereby intensified, were responsible for the most powerful geomagnetic storm since November 2003. Users of Global Navigation Satellite Systems (GNSS), such as GPS or Galileo, rely on satellite signals being received without interference and that the signal delay caused by free electrons and ions in the atmosphere can be sufficiently modeled. The solar storms in May 2024 significantly impacted the ionosphere's composition, particularly the mean electron density and fluctuations in the ionospheric plasma. This presentation demonstrates the impact of the storm on GNSS signal reception, specifically for users in Austria, and examines how well common ionospheric models, such as Klobuchar and NeQuick G, were able to compensate for storm-induced anomalies in GNSS signal propagation. The resulting effects on the accuracy and convergence time of GNSS users' Positioning, Navigation, and Timing (PNT) solutions are also discussed.