client.go          | 6 +++---
 tracker/http.go    | 2 +-
 tracker/tracker.go | 5 +++--

diff --git a/client.go b/client.go
index 16ded0d795a5d8cbd60bc6506f02152e5e4881d2..30e6aa30c6317527d38339a683d9218fd0b7c8f7 100644
--- a/client.go
+++ b/client.go
@@ -2514,7 +2514,7 @@ func (cl *Client) announceTorrentTrackers(t *torrent) {
 	req := tracker.AnnounceRequest{
 		Event:    tracker.Started,
 		NumWant:  -1,
-		Port:     int16(cl.incomingPeerPort()),
+		Port:     uint16(cl.incomingPeerPort()),
 		PeerId:   cl.peerID,
 		InfoHash: t.InfoHash,
 	}
@@ -2522,7 +2522,7 @@ 	if !cl.waitWantPeers(t) {
 		return
 	}
 	cl.mu.RLock()
-	req.Left = t.bytesLeft()
+	req.Left = uint64(t.bytesLeft())
 	trackers := t.Trackers
 	cl.mu.RUnlock()
 	if cl.announceTorrentTrackersFastStart(&req, trackers, t) {
@@ -2531,7 +2531,7 @@ 	}
 newAnnounce:
 	for cl.waitWantPeers(t) {
 		cl.mu.RLock()
-		req.Left = t.bytesLeft()
+		req.Left = uint64(t.bytesLeft())
 		trackers = t.Trackers
 		cl.mu.RUnlock()
 		numTrackersTried := 0
diff --git a/tracker/http.go b/tracker/http.go
index 0a65fc707bd8ec3d59c628df65744fc188607060..97a045a98609c31ed218ac22ebc1747bd4849fa1 100644
--- a/tracker/http.go
+++ b/tracker/http.go
@@ -63,7 +63,7 @@ 	q.Set("peer_id", string(ar.PeerId[:]))
 	q.Set("port", fmt.Sprintf("%d", ar.Port))
 	q.Set("uploaded", strconv.FormatInt(ar.Uploaded, 10))
 	q.Set("downloaded", strconv.FormatInt(ar.Downloaded, 10))
-	q.Set("left", strconv.FormatInt(ar.Left, 10))
+	q.Set("left", strconv.FormatUint(ar.Left, 10))
 	if ar.Event != None {
 		q.Set("event", ar.Event.String())
 	}
diff --git a/tracker/tracker.go b/tracker/tracker.go
index 98a77a182c247e54ed2ae4b9e6b6c36a93a9c59f..c54aae0f04e5cede773258050c144defc918788d 100644
--- a/tracker/tracker.go
+++ b/tracker/tracker.go
@@ -6,17 +6,18 @@ 	"net"
 	"net/url"
 )
 
+// Marshalled as binary by the UDP client, so be careful making changes.
 type AnnounceRequest struct {
 	InfoHash   [20]byte
 	PeerId     [20]byte
 	Downloaded int64
-	Left       int64
+	Left       uint64
 	Uploaded   int64
 	Event      AnnounceEvent
 	IPAddress  int32
 	Key        int32
 	NumWant    int32 // How many peer addresses are desired. -1 for default.
-	Port       int16
+	Port       uint16
 } // 82 bytes
 
 type AnnounceResponse struct {