diff --git a/ChangeLog b/ChangeLog
index 54496924..b58ce2f3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2011-11-29  Mats Erik Andersson <gnu@gisladisker.se>
+
+	* whois/make_ip_del.pl: Compute netmasks correctly
+	also with 64-bit arithmetic.
+
 2011-11-26  Mats Erik Andersson <gnu@gisladisker.se>
 
 	* tests/tftp.sh: Return skip code if INET port is already in use.
diff --git a/whois/make_ip_del.pl b/whois/make_ip_del.pl
index cd98cf16..89ffaa55 100755
--- a/whois/make_ip_del.pl
+++ b/whois/make_ip_del.pl
@@ -29,7 +29,7 @@ while (<>) {
 	my $m=$2; my $s=$3;
 	my ($i1, $i2, $i3, $i4)=split(/\./, $1);
 	print "{ ".(($i1<<24)+($i2<<16)+($i3<<8)+$i4)."UL, ".
-		(~(0xffffffff>>$m))."UL, \"";
+		(0xffffffff^(0xffffffff>>$m))."UL, \"";
 	if ($s =~ /\./) {
 		print "$s";
 	} else {