open stamp file for writing instead of updating {a,m}time because the former will also create the stamp if it does not yet exist
--- a/bin/update-serial	Fri May 27 13:13:38 2011 +0200
+++ b/bin/update-serial	Fri May 27 13:16:34 2011 +0200
@@ -240,9 +240,7 @@
     $serial =~ s/\s*//g;
     say " * $zone: serial incremented to $serial";
 
-    my ($atime, $utime) = (time) x 2; 
-    my $s = (dirname $file) . '/.stamp';
-    utime $atime, $utime, $s or die "Can't 'utime $atime, $utime, $s': $!";
+    open(my $stamp, ">", dirname($file) . "/.stamp");
 
     say " * $zone: stamp aktualisiert";
 #    say " XXX $zone: stamp '$s' aktualisiert";