diff --git a/defaults.go b/defaults.go
index 1778b1ca..15fd8c02 100644
--- a/defaults.go
+++ b/defaults.go
@@ -244,12 +244,19 @@ func ReverseAddr(addr string) (arpa string, err error) {
 	if ip == nil {
 		return "", &Error{err: "unrecognized address: " + addr}
 	}
-	if ip.To4() != nil {
-		return strconv.Itoa(int(ip[15])) + "." + strconv.Itoa(int(ip[14])) + "." + strconv.Itoa(int(ip[13])) + "." +
-			strconv.Itoa(int(ip[12])) + ".in-addr.arpa.", nil
+	if v4 := ip.To4(); v4 != nil {
+		buf := make([]byte, 0, net.IPv4len*4+len("in-addr.arpa."))
+		// Add it, in reverse, to the buffer
+		for i := len(v4) - 1; i >= 0; i-- {
+			buf = strconv.AppendInt(buf, int64(v4[i]), 10)
+			buf = append(buf, '.')
+		}
+		// Append "in-addr.arpa." and return (buf already has the final .)
+		buf = append(buf, "in-addr.arpa."...)
+		return string(buf), nil
 	}
 	// Must be IPv6
-	buf := make([]byte, 0, len(ip)*4+len("ip6.arpa."))
+	buf := make([]byte, 0, net.IPv6len*4+len("ip6.arpa."))
 	// Add it, in reverse, to the buffer
 	for i := len(ip) - 1; i >= 0; i-- {
 		v := ip[i]
diff --git a/dns_bench_test.go b/dns_bench_test.go
index d1f1002a..a34fe994 100644
--- a/dns_bench_test.go
+++ b/dns_bench_test.go
@@ -342,3 +342,29 @@ func BenchmarkIdGeneration(b *testing.B) {
 		_ = id()
 	}
 }
+
+func BenchmarkReverseAddr(b *testing.B) {
+	b.Run("IP4", func(b *testing.B) {
+		for n := 0; n < b.N; n++ {
+			addr, err := ReverseAddr("192.0.2.1")
+			if err != nil {
+				b.Fatal(err)
+			}
+			if expect := "1.2.0.192.in-addr.arpa."; addr != expect {
+				b.Fatalf("invalid reverse address, expected %q, got %q", expect, addr)
+			}
+		}
+	})
+
+	b.Run("IP6", func(b *testing.B) {
+		for n := 0; n < b.N; n++ {
+			addr, err := ReverseAddr("2001:db8::68")
+			if err != nil {
+				b.Fatal(err)
+			}
+			if expect := "8.6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa."; addr != expect {
+				b.Fatalf("invalid reverse address, expected %q, got %q", expect, addr)
+			}
+		}
+	})
+}