  Hubble Space Telescope (HST) WFPC2 archival images obtained years prior to
the explosion of the Type II-plateau supernova (SN) 2001du in NGC 1365
previously have been analyzed to isolate the progenitor star. The SN site was
located using precise astrometry applied to the HST images, with significant
uncertainty, leaving three possible progenitor candidates. Images of the fading
SN have recently become publicly available in the HST archive, allowing us to
pinpoint the SN's exact location on the pre-explosion images. We show that the
SN occurred in very close proximity to one of the blue candidate stars, but we
argue that this star is not the actual progenitor. Instead, the progenitor was
not detected on the pre-SN images, and we constrain the progenitor's mass to be
less than 13 (+7, -4) Msuns. This is consistent with previous constraints on
the progenitor masses of other Type II-plateau supernovae (SNe), suggesting
that such SNe arise from the iron core collapse of massive stars at the lower
extreme of the possible mass range.
