Rapid magnitude estimate procedures represent a crucial part of proposed earthquake early warning systems. Most of these estimates are focused on the first part of the P-wave train, the earlier and less destructive part of the ground motion that follows an earthquake. Allen and Kanamori (Science 300:786-789, 2003 ) proposed to use the predominant period of the P-wave to determine the magnitude of a large earthquake at local distance and Olivieri et al. (Bull Seismol Soc Am 185:74-81, 2008 ) calibrated a specific relation for the Italian region. The Mw 6.3 earthquake hit Central Italy on April 6, 2009 and the largest aftershocks provide a useful dataset to validate the proposed relation and discuss the risks connected to the extrapolation of magnitude relations with a poor dataset of large earthquake waveforms. A large discrepancy between local magnitude (ML) estimated by means of tau^sub p^^sup max^ evaluation and standard ML (6.8 ± 1.5 vs. 5.9 ± 0.4) suggests using caution when ML vs. tau^sub p^^sup max^ calibrations do not include a relevant dataset of large earthquakes. Effects from large residuals could be mitigated or removed introducing selection rules on tau^sub p^ function, by regionalizing the ML vs. tau^sub p^^sup max^ function in the presence of significant tectonic or geological heterogeneity, and using probabilistic and evolutionary methods.PUBLICATION ABSTRACT