  A theorem of Paul Roberts states that the integral closure of a regular local
ring in a generically abelian extension is Cohen-Macaulay, provided the
characteristic of the residue field does not divide the order of the Galois
group. An example of Koh shows the conclusion is false in the modular case.
After a modification to the statement concerning ramification over $p$ in
codimension one, we give an extension of Roberts's theorem to the modular case
for unramified regular local rings in mixed characteristic when the $p$-torsion
of the Galois group is annihilated by $p$.
