diff --git a/exp/audio/vorbis/vorbis.go b/exp/audio/vorbis/vorbis.go
index dae486974..67f65a703 100644
--- a/exp/audio/vorbis/vorbis.go
+++ b/exp/audio/vorbis/vorbis.go
@@ -27,11 +27,11 @@ import (
 	"github.com/hajimehoshi/go-vorbis"
 )
 
-type Stream struct {
+type stream struct {
 	buf *bytes.Reader
 }
 
-func Decode(context *audio.Context, src io.Reader) (*Stream, error) {
+func Decode(context *audio.Context, src io.Reader) (io.ReadSeeker, error) {
 	decoded, channels, sampleRate, err := vorbis.Decode(src)
 	if err != nil {
 		return nil, err
@@ -48,16 +48,16 @@ func Decode(context *audio.Context, src io.Reader) (*Stream, error) {
 	if err != nil {
 		return nil, err
 	}
-	s := &Stream{
+	s := &stream{
 		buf: bytes.NewReader(b),
 	}
 	return s, nil
 }
 
-func (s *Stream) Read(p []byte) (int, error) {
+func (s *stream) Read(p []byte) (int, error) {
 	return s.buf.Read(p)
 }
 
-func (s *Stream) Seek(offset int64, whence int) (int64, error) {
+func (s *stream) Seek(offset int64, whence int) (int64, error) {
 	return s.buf.Seek(offset, whence)
 }
diff --git a/exp/audio/vorbis/vorbis_js.go b/exp/audio/vorbis/vorbis_js.go
index 6080dc14d..bdf0052ba 100644
--- a/exp/audio/vorbis/vorbis_js.go
+++ b/exp/audio/vorbis/vorbis_js.go
@@ -25,19 +25,19 @@ import (
 	"github.com/hajimehoshi/ebiten/exp/audio"
 )
 
-type Stream struct {
+type stream struct {
 	buf *bytes.Reader
 }
 
 // TODO: This just uses decodeAudioData can treat audio files other than Ogg/Vorbis.
 // TODO: This doesn't work on iOS which doesn't have Ogg/Vorbis decoder.
 
-func Decode(context *audio.Context, src io.Reader) (*Stream, error) {
+func Decode(context *audio.Context, src io.Reader) (io.ReadSeeker, error) {
 	b, err := ioutil.ReadAll(src)
 	if err != nil {
 		return nil, err
 	}
-	s := &Stream{}
+	s := &stream{}
 	ch := make(chan struct{})
 
 	// TODO: 1 is a correct second argument?
@@ -61,10 +61,10 @@ func Decode(context *audio.Context, src io.Reader) (*Stream, error) {
 	return s, nil
 }
 
-func (s *Stream) Read(p []byte) (int, error) {
+func (s *stream) Read(p []byte) (int, error) {
 	return s.buf.Read(p)
 }
 
-func (s *Stream) Seek(offset int64, whence int) (int64, error) {
+func (s *stream) Seek(offset int64, whence int) (int64, error) {
 	return s.buf.Seek(offset, whence)
 }