diff --git a/internal/radio/song.go b/internal/radio/song.go
index 074b7e1..ba4ef47 100644
--- a/internal/radio/song.go
+++ b/internal/radio/song.go
@@ -39,6 +39,8 @@ func (s *Song) MarshalJSON() ([]byte, error) {
 		StartAt:      s.StartAt.UTC().Format(time.RFC3339)})
 }
 
+// SongList holds a currently playing song and a list of previously played ones
+// with a maximal length of maxLen.
 type SongList struct {
 	sync.RWMutex
 	current   Song
@@ -69,7 +71,7 @@ func (sl *SongList) Add(newSong Song) {
 	sl.current = newSong
 }
 
-// Current returns a currently playing song.
+// Current returns a currently playing song or nil if it isn't set yet.
 func (sl *SongList) Current() *Song {
 	sl.RLock()
 	defer sl.RUnlock()
@@ -101,7 +103,7 @@ func (sl *SongList) List() []Song {
 	return sl.lastSongs
 }
 
-// MaxLen returns a maximal length of a list
+// MaxLen returns a maximal length of a song list.
 func (sl *SongList) MaxLen() int {
 	return sl.maxLen
 }