tracker/tracker.go |  2 +-
 tracker/udp.go     | 10 ++++++++--

diff --git a/tracker/tracker.go b/tracker/tracker.go
index fd24b0bef77e1ca549acf72896f7446166b134cb..95f6ed1e29c131c0e598942154b0046affd4f1a5 100644
--- a/tracker/tracker.go
+++ b/tracker/tracker.go
@@ -18,7 +18,7 @@ 	Uploaded   int64
 	// Apparently this is optional. None can be used for announces done at
 	// regular intervals.
 	Event     AnnounceEvent
-	IPAddress int32
+	IPAddress uint32
 	Key       int32
 	NumWant   int32 // How many peer addresses are desired. -1 for default.
 	Port      uint16
diff --git a/tracker/udp.go b/tracker/udp.go
index babbbefb05cb12fc2da3dc81372a267c8df403d7..656cc7df5c551797d413ca0a1a491095bd495d09 100644
--- a/tracker/udp.go
+++ b/tracker/udp.go
@@ -99,12 +99,18 @@ 	rip := missinggo.AddrIP(c.socket.RemoteAddr())
 	return rip.To16() != nil && rip.To4() == nil
 }
 
-func (c *udpAnnounce) Do(req *AnnounceRequest) (res AnnounceResponse, err error) {
+func (c *udpAnnounce) Do(req AnnounceRequest) (res AnnounceResponse, err error) {
 	err = c.connect()
 	if err != nil {
 		return
 	}
 	reqURI := c.url.RequestURI()
+	if c.ipv6() {
+		// BEP 15
+		req.IPAddress = 0
+	} else if req.IPAddress == 0 && c.a.ClientIp4.IP != nil {
+		req.IPAddress = binary.BigEndian.Uint32(c.a.ClientIp4.IP.To4())
+	}
 	// Clearly this limits the request URI to 255 bytes. BEP 41 supports
 	// longer but I'm not fussed.
 	options := append([]byte{optionTypeURLData, byte(len(reqURI))}, []byte(reqURI)...)
@@ -288,5 +294,5 @@ 		url: *_url,
 		a:   &opt,
 	}
 	defer ua.Close()
-	return ua.Do(&opt.Request)
+	return ua.Do(opt.Request)
 }