diff --git a/encoder.go b/encoder.go
index b9fb199..727477a 100644
--- a/encoder.go
+++ b/encoder.go
@@ -264,8 +264,16 @@ func (e *Encoder) WriteUint128(i Uint128, order binary.ByteOrder) (err error) {
 		zlog.Debug("encode: write uint128", zap.Stringer("hex", i), zap.Uint64("lo", i.Lo), zap.Uint64("hi", i.Hi))
 	}
 	buf := make([]byte, TypeSize.Uint128)
-	order.PutUint64(buf, i.Lo)
-	order.PutUint64(buf[TypeSize.Uint64:], i.Hi)
+	switch order {
+	case binary.LittleEndian:
+		order.PutUint64(buf[:8], i.Lo)
+		order.PutUint64(buf[8:], i.Hi)
+	case binary.BigEndian:
+		order.PutUint64(buf[:8], i.Hi)
+		order.PutUint64(buf[8:], i.Lo)
+	default:
+		return fmt.Errorf("invalid byte order: %v", order)
+	}
 	return e.toWriter(buf)
 }
 
@@ -274,8 +282,16 @@ func (e *Encoder) WriteInt128(i Int128, order binary.ByteOrder) (err error) {
 		zlog.Debug("encode: write int128", zap.Stringer("hex", i), zap.Uint64("lo", i.Lo), zap.Uint64("hi", i.Hi))
 	}
 	buf := make([]byte, TypeSize.Uint128)
-	order.PutUint64(buf, i.Lo)
-	order.PutUint64(buf[TypeSize.Uint64:], i.Hi)
+	switch order {
+	case binary.LittleEndian:
+		order.PutUint64(buf[:8], i.Lo)
+		order.PutUint64(buf[8:], i.Hi)
+	case binary.BigEndian:
+		order.PutUint64(buf[:8], i.Hi)
+		order.PutUint64(buf[8:], i.Lo)
+	default:
+		return fmt.Errorf("invalid byte order: %v", order)
+	}
 	return e.toWriter(buf)
 }
 
diff --git a/encoder_test.go b/encoder_test.go
index e41df51..72bf966 100644
--- a/encoder_test.go
+++ b/encoder_test.go
@@ -439,8 +439,8 @@ func TestEncoder_Uint128(t *testing.T) {
 	enc.WriteUint128(u, BE)
 
 	assert.Equal(t, []byte{
-		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x07,
 		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x09,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x07,
 	}, buf.Bytes())
 }