  We discuss the different Kimber-Martin-Ryskin (KMR) prescriptions for
unintegrated parton distribution functions (uPDFs). We show that the
strong-ordering (SO) and the angular-ordering (AO) cut-offs lead to strong
discrepancies between the obtained cross sections. While the result obtained
with the AO cut-off overestimates the heavy-flavor cross section by about a
factor 3, the SO cut-off gives the correct answer. We also solve the issue of
the KMR uPDFs definitions mentioned by Golec-Biernat and Sta\'sto, and show
that, in the case of the AO cut-off, the KMR uPDFs are ill-defined.
