metainfo/announcelist.go | 27 +++++++++++++++++++++++++++
 metainfo/metainfo.go     | 23 +++++++++++++++--------

diff --git a/metainfo/announcelist.go b/metainfo/announcelist.go
new file mode 100644
index 0000000000000000000000000000000000000000..3a5c09d48349f896134b4ba7e0cb7429d3553853
--- /dev/null
+++ b/metainfo/announcelist.go
@@ -0,0 +1,27 @@
+package metainfo
+
+type AnnounceList [][]string
+
+// Whether the AnnounceList should be preferred over a single URL announce.
+func (al AnnounceList) OverridesAnnounce(announce string) bool {
+	for _, tier := range al {
+		for _, url := range tier {
+			if url != "" || announce == "" {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (al AnnounceList) DistinctValues() (ret map[string]struct{}) {
+	for _, tier := range al {
+		for _, v := range tier {
+			if ret == nil {
+				ret = make(map[string]struct{})
+			}
+			ret[v] = struct{}{}
+		}
+	}
+	return
+}
diff --git a/metainfo/metainfo.go b/metainfo/metainfo.go
index decfc3a001aac6fa6ee53efcb4d0ff261a79d6fb..947bd7136b0e9d61e8ab9522853ff485fd92d633 100644
--- a/metainfo/metainfo.go
+++ b/metainfo/metainfo.go
@@ -11,7 +11,7 @@
 type MetaInfo struct {
 	InfoBytes    bencode.Bytes `bencode:"info"`
 	Announce     string        `bencode:"announce,omitempty"`
-	AnnounceList [][]string    `bencode:"announce-list,omitempty"`
+	AnnounceList AnnounceList  `bencode:"announce-list,omitempty"`
 	Nodes        []Node        `bencode:"nodes,omitempty"`
 	CreationDate int64         `bencode:"creation date,omitempty"`
 	Comment      string        `bencode:"comment,omitempty"`
@@ -66,15 +66,22 @@ }
 
 // Creates a Magnet from a MetaInfo.
 func (mi *MetaInfo) Magnet(displayName string, infoHash Hash) (m Magnet) {
-	for _, tier := range mi.AnnounceList {
-		for _, tracker := range tier {
-			m.Trackers = append(m.Trackers, tracker)
-		}
-	}
-	if m.Trackers == nil && mi.Announce != "" {
-		m.Trackers = []string{mi.Announce}
+	for t := range mi.UpvertedAnnounceList().DistinctValues() {
+		m.Trackers = append(m.Trackers, t)
 	}
 	m.DisplayName = displayName
 	m.InfoHash = infoHash
 	return
 }
+
+// Returns the announce list converted from the old single announce field if
+// necessary.
+func (mi *MetaInfo) UpvertedAnnounceList() AnnounceList {
+	if mi.AnnounceList.OverridesAnnounce(mi.Announce) {
+		return mi.AnnounceList
+	}
+	if mi.Announce != "" {
+		return [][]string{[]string{mi.Announce}}
+	}
+	return nil
+}