  We systematically explore the influence of the prior of the peak absolute
magnitude ($M$) of type Ia supernovae (SNe Ia) on the measurement of the Hubble
constant ($H_0$) from SNe Ia observations. We consider five different
data-motivated $M$ priors, representing varying levels of dispersion, and
assume the spatially-flat $\Lambda$CDM cosmological model. Different $M$ priors
lead to relative changes in the mean values of $H_0$ from 2% to 7%. Loose
priors on $M$ yield $H_0$ estimates consistent with both the Planck 2018 result
and the SH0ES result at the 68% confidence level. We also examine the potential
impact of peculiar velocity subtraction on the value of $H_0$, and show that it
is insignificant for the SNe Ia observations with redshift $z > 0.01$ used in
our analyses. We also repeat the analysis in the cosmography model and find
very similar results. This suggests that our results are robust and model
independent.
