diff --git a/dns/axfr.pl b/dns/axfr.pl
index 5f8cfc4..432866c 100755
--- a/dns/axfr.pl
+++ b/dns/axfr.pl
@@ -2,6 +2,13 @@
 use strict;
 use Net::DNS;
 
+sub usage {
+    print STDERR "Usage: $0 zone nameserver\n" unless (@ARGV == 2);
+    exit(1);
+}
+
+usage() unless (@ARGV == 2);
+
 my $res = new Net::DNS::Resolver;
 $res->nameservers($ARGV[1]);
 my @zone = $res->axfr($ARGV[0]);