  Constructing charges in the covariant phase space formalism often leads to
formally divergent expressions, even when the fields satisfy physically
acceptable fall-off conditions. These expressions can be rendered finite by
corner ambiguities in the definition of the presymplectic potential, which in
some cases may be motivated by arguments involving boundary Lagrangians. We
show that the necessary corner terms are already present in the variation of
the bulk action and can be extracted in a straightforward way. Once these
corner terms are included in the presymplectic potential, charges derived from
an associated codimension-2 form are automatically finite. We illustrate the
procedure with examples in two and three dimensions, working in Bondi gauge and
obtaining integrable charges. As a by-product, actions are derived for these
theories that admit a well-defined variational principle when the fields
satisfy boundary conditions on a timelike surface with corners. An interesting
feature of our analysis is that the fields are not required to be fully
on-shell.
