  The dependence of the top-quark mass measurement in top-quark pair production
on the parton distribution functions (PDF) is explored through differential
mass distributions in $t\bar{t}$ and $t\bar{t}j$ production at the LHC and a
future 100 TeV proton-proton collider. The top-quark mass uncertainty is
obtained from chi-squared fits to invariant mass distributions from simulations
assuming different top pole masses around the nominal value of 172.5 GeV. The
PDF uncertainties of the differential distributions are used in the chi-square
evaluation and reduced through a fit to differential distributions in
$t\bar{t}$ and $t\bar{t}j$ production.
