diff --git a/DEVEL/hooksdir/nhsub b/DEVEL/hooksdir/nhsub
index c169609be..a1686bd24 100644
--- a/DEVEL/hooksdir/nhsub
+++ b/DEVEL/hooksdir/nhsub
@@ -5,7 +5,7 @@
 # Note: was originally called nhdate; the rename is not reflected in the code.
 
 use strict;
-my %opt;	#cmd v n f F (other single char, but we don't care)
+our %opt;	#cmd v n f F m (other single char, but we don't care)
 my $mode;	# a c d f (add, commit, date, date -f)
 
 if(length $ENV{GIT_PREFIX}){
@@ -249,7 +249,6 @@ my $count = s/\$$PREFIX-(([A-Za-z][A-Za-z0-9_]*)(: ([^\x24]+))?)\$/&handlevar($2
 	my $ofile = $file . ".nht";
 	open(TOUT, ">", $ofile) or die "Can't open $ofile";
 
-#XXX MUST add a loop here
 #	die "write failed: $!" unless defined syswrite(TOUT, $_);
 	my $offset = 0;
 	my $sent;
@@ -267,7 +266,7 @@ my $count = s/\$$PREFIX-(([A-Za-z][A-Za-z0-9_]*)(: ([^\x24]+))?)\$/&handlevar($2
 	rename $ofile, $file or die "Can't rename $ofile to $file";
 }
 
-# XXX docs for --fixup and --squash are wrong in synopsis. --file missing
+# XXX docs for --fixup and --squash are wrong in git's synopsis. --file missing
 #   --message --template -t
 sub cmdparse {
 	my(@in) = @_;
@@ -305,11 +304,15 @@ sub cmdparse {
 			shift @in;
 			next;
 		}
+# XXX this is messy - time for a rewrite?
 		if(m/^-(.*)/){
 			foreach my $single ( split(//,$1) ){
 					# don't do -v here from add/commit
 				if($single ne 'v'){
-					$opt{$single}++;
+					# don't use -m from add/commit
+					if($opt{cmd} eq 'date' || $single ne 'm'){
+						$opt{$single}++;
+					}
 				} elsif($opt{cmd} eq 'date'){
 					$opt{$single}++;
 				}
@@ -408,8 +411,14 @@ use POSIX qw(strftime);
 # On pull, keep the current value so we can see the last change date.
 sub Date {
 	my($val) = @_;
-	# we add this to make merge easier for now XXX
-	my $now = time; # not %s below - may not be portable
+	my $now;
+	if($opt{m}){
+		my $hash = `git log -1 '--format=format:%H' $::current_file`;
+			#author keni <keni@his.com> 1429884677 -0400
+		chomp($now = `git cat-file -p $hash | awk '/author/{print \$4}'`);
+	} else {
+		$now = time;
+	}
 	# YYYY/MM/DD HH:MM:SS
 	$val = "$now " . strftime("%Y/%m/%d %H:%M:%S", gmtime($now));
 	return $val;
@@ -448,7 +457,7 @@ C<nhsub> - NetHack git command for substitution variables
 
 =head1 SYNOPSIS
 
-C<git nhsub [-v[v[v]] [-n] [-f|-F] [--] [file...]>
+C<git nhsub [-v[v[v]] [-n] [-f|-F] [-m] [--] [file...]>
 
 =head1 DESCRIPTION
 
@@ -498,4 +507,11 @@ even if the NHSUBST attribute is not set for the
 file, and only if the file is not ignored by git.  Not available
 when invoked as part of C<nhadd> or C<nhcommit>.
 
+=item C<-m>
+
+Use metadata (C<git log> and C<git cat-file>) to find the last change date to
+substitute.  Often used with C<-f>.  This is useful for cleaning up dates in files that were not
+updated when last changed. (Do not use C<git nhadd>/C<git nhcommit> after C<nhsub -m>
+or the changes will be overwritten with the current date.)
+
 =back