diff --git a/connection.go b/connection.go
index 85aaabdc..a019ff20 100644
--- a/connection.go
+++ b/connection.go
@@ -76,6 +76,10 @@ type connection struct {
 	Choked           bool
 	requests         map[request]struct{}
 	requestsLowWater int
+	// Chunks that we might reasonably expect to receive from the peer. Due to
+	// latency, buffering, and implementation differences, we may receive
+	// chunks that are no longer in the set of requests actually want.
+	validReceiveChunks map[request]struct{}
 	// Indexed by metadata piece, set to true if posted and pending a
 	// response.
 	metadataRequests []bool
@@ -475,9 +479,6 @@ type messageWriter func(pp.Message) bool
 
 // Proxies the messageWriter's response.
 func (cn *connection) request(r request, mw messageWriter) bool {
-	if cn.requests == nil {
-		cn.requests = make(map[request]struct{}, cn.nominalMaxRequests())
-	}
 	if _, ok := cn.requests[r]; ok {
 		panic("chunk already requested")
 	}
@@ -497,7 +498,14 @@ func (cn *connection) request(r request, mw messageWriter) bool {
 			panic("requesting while choked and not allowed fast")
 		}
 	}
+	if cn.requests == nil {
+		cn.requests = make(map[request]struct{})
+	}
 	cn.requests[r] = struct{}{}
+	if cn.validReceiveChunks == nil {
+		cn.validReceiveChunks = make(map[request]struct{})
+	}
+	cn.validReceiveChunks[r] = struct{}{}
 	cn.t.pendingRequests[r]++
 	cn.t.lastRequested[r] = time.Now()
 	cn.updateExpectingChunks()
@@ -1099,6 +1107,7 @@ func (c *connection) mainReadLoop() (err error) {
 			c.updateExpectingChunks()
 		case pp.Reject:
 			c.deleteRequest(newRequestFromMessage(&msg))
+			delete(c.validReceiveChunks, newRequestFromMessage(&msg))
 		case pp.Unchoke:
 			c.PeerChoked = false
 			c.tickleWriter()
@@ -1126,7 +1135,7 @@ func (c *connection) mainReadLoop() (err error) {
 		case pp.HaveNone:
 			err = c.peerSentHaveNone()
 		case pp.Piece:
-			c.receiveChunk(&msg)
+			err = c.receiveChunk(&msg)
 			if len(msg.Piece) == int(t.chunkSize) {
 				t.chunkPool.Put(&msg.Piece)
 			}
@@ -1271,13 +1280,18 @@ func (cn *connection) rw() io.ReadWriter {
 }
 
 // Handle a received chunk from a peer.
-func (c *connection) receiveChunk(msg *pp.Message) {
+func (c *connection) receiveChunk(msg *pp.Message) error {
 	t := c.t
 	cl := t.cl
 	torrent.Add("chunks received", 1)
 
 	req := newRequestFromMessage(msg)
 
+	if _, ok := c.validReceiveChunks[req]; !ok {
+		return errors.New("received unexpected chunk")
+	}
+	delete(c.validReceiveChunks, req)
+
 	// Request has been satisfied.
 	if c.deleteRequest(req) {
 		if c.expectingChunks() {
@@ -1299,7 +1313,7 @@ func (c *connection) receiveChunk(msg *pp.Message) {
 	if t.haveChunk(req) {
 		torrent.Add("chunks received unwanted", 1)
 		c.allStats(add(1, func(cs *ConnStats) *Count { return &cs.ChunksReadUnwanted }))
-		return
+		return nil
 	}
 
 	index := int(req.Index)
@@ -1343,7 +1357,7 @@ func (c *connection) receiveChunk(msg *pp.Message) {
 		log.Printf("%s (%s): error writing chunk %v: %s", t, t.infoHash, req, err)
 		t.pendRequest(req)
 		t.updatePieceCompletion(int(msg.Index))
-		return
+		return nil
 	}
 
 	// It's important that the piece is potentially queued before we check if
@@ -1357,6 +1371,8 @@ func (c *connection) receiveChunk(msg *pp.Message) {
 
 	cl.event.Broadcast()
 	t.publishPieceChange(int(req.Index))
+
+	return nil
 }
 
 func (c *connection) onDirtiedPiece(piece int) {