diff --git a/main.go b/main.go
index ae6eef8..1a95741 100644
--- a/main.go
+++ b/main.go
@@ -26,6 +26,8 @@ var (
 )
 
 func genRecord() (libdns.Record, error) {
+	ipv4 := ip.To4()
+	ipv6 := ip.To16()
 	switch {
 	case cname != "":
 		return libdns.Record{
@@ -33,17 +35,17 @@ func genRecord() (libdns.Record, error) {
 			Name:  sub,
 			Value: cname,
 		}, nil
-	case len(ip) == net.IPv4len:
+	case ipv4 != nil:
 		return libdns.Record{
 			Type:  "A",
 			Name:  sub,
-			Value: ip.To4().String(),
+			Value: ipv4.String(),
 		}, nil
-	case len(ip) == net.IPv6len:
+	case ipv6 != nil:
 		return libdns.Record{
 			Type:  "AAAA",
 			Name:  sub,
-			Value: ip.To16().String(),
+			Value: ipv6.String(),
 		}, nil
 	}
 	return libdns.Record{}, fmt.Errorf("neither cname nor valid ip is set")
diff --git a/main_test.go b/main_test.go
index cc8f23b..b162245 100644
--- a/main_test.go
+++ b/main_test.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"net"
 	"testing"
 )
 
@@ -9,7 +10,29 @@ func TestParseRange(t *testing.T) {
 	expected := []int{0, 1, 2, 6}
 	actual := parseRange("0-2,-5,6,-7-7,1, 11", 10)
 	if fmt.Sprint(expected) != fmt.Sprint(actual) {
-		fmt.Printf("unexpected %#v\n", actual)
-		t.Fail()
+		t.Errorf("unexpected %#v\n", actual)
+	}
+}
+
+func TestParseIP(t *testing.T) {
+	var ip net.IP
+	if err := ip.UnmarshalText([]byte("127.0.0.1")); err != nil {
+		t.Error(err)
+	}
+	if ip.To4() == nil {
+		t.Error("Failed to parse ipv4")
+	}
+	if ip.To16() == nil {
+		t.Error("Failed to parse as ipv6")
+	}
+
+	if err := ip.UnmarshalText([]byte("::1")); err != nil {
+		t.Error(err)
+	}
+	if ip.To16() == nil {
+		t.Error("Failed to parse ipv6")
+	}
+	if ip.To4() != nil {
+		t.Error("ipv6 parsed as ipv4")
 	}
 }