client.go     |  1 +
 connection.go |  2 +-
 torrent.go    | 81 +++++++++++++++++++++++++----------------------------

diff --git a/client.go b/client.go
index 8c356eea324b2dc1981eb442f30d4d079d739511..c457bef6c85d4db12afef1f0cb5df88a4296a769 100644
--- a/client.go
+++ b/client.go
@@ -1147,6 +1147,7 @@ 	t = &Torrent{
 		cl:       cl,
 		infoHash: ih,
 		peers:    make(map[peersKey]Peer),
+		conns:    make(map[*connection]struct{}, 2*defaultEstablishedConnsPerTorrent),
 
 		halfOpen:          make(map[string]struct{}),
 		pieceStateChanges: pubsub.NewPubSub(),
diff --git a/connection.go b/connection.go
index 06cb7ca8fb3ba312fc1ddc828ab0603daead393a..3ba41076fbe3ba895adc0a754e08dd6b84c04a4b 100644
--- a/connection.go
+++ b/connection.go
@@ -964,7 +964,7 @@ 	// Record that we have the chunk.
 	piece.unpendChunkIndex(chunkIndex(req.chunkSpec, t.chunkSize))
 
 	// Cancel pending requests for this chunk.
-	for _, c := range t.conns {
+	for c := range t.conns {
 		if cl.connCancel(t, c, req) {
 			c.updateRequests()
 		}
diff --git a/torrent.go b/torrent.go
index c2baf9c10dd5a0eeaf2421d8488776f53122592c..f6f723bf42b74a5eb553f442ec4161a77830ff49 100644
--- a/torrent.go
+++ b/torrent.go
@@ -66,7 +66,7 @@
 	// The info dict. nil if we don't have it (yet).
 	info *metainfo.Info
 	// Active peer connections, running message stream loops.
-	conns               []*connection
+	conns               map[*connection]struct{}
 	maxEstablishedConns int
 	// Set of addrs to which we're attempting to connect. Connections are
 	// half-open until all handshakes are completed.
@@ -140,7 +140,7 @@ 	return t.pieces[piece].Storage().GetIsComplete()
 }
 
 func (t *Torrent) numConnsUnchoked() (num int) {
-	for _, c := range t.conns {
+	for c := range t.conns {
 		if !c.PeerChoked {
 			num++
 		}
@@ -153,7 +153,7 @@ func (t *Torrent) addrActive(addr string) bool {
 	if _, ok := t.halfOpen[addr]; ok {
 		return true
 	}
-	for _, c := range t.conns {
+	for c := range t.conns {
 		if c.remoteAddr().String() == addr {
 			return true
 		}
@@ -163,7 +163,7 @@ }
 
 func (t *Torrent) worstUnclosedConns() (ret []*connection) {
 	ret = make([]*connection, 0, len(t.conns))
-	for _, c := range t.conns {
+	for c := range t.conns {
 		if !c.closed.IsSet() {
 			ret = append(ret, c)
 		}
@@ -278,7 +278,7 @@ 	}
 	t.metadataBytes = b
 	t.metadataCompletedChunks = nil
 	t.makePieces()
-	for _, conn := range t.conns {
+	for conn := range t.conns {
 		if err := conn.setNumPieces(t.numPieces()); err != nil {
 			log.Printf("closing connection: %s", err)
 			conn.Close()
@@ -325,7 +325,7 @@ 		return
 	}
 	t.metadataBytes = make([]byte, bytes)
 	t.metadataCompletedChunks = make([]bool, (bytes+(1<<14)-1)/(1<<14))
-	for _, c := range t.conns {
+	for c := range t.conns {
 		c.requestPendingMetadata()
 	}
 	return
@@ -477,8 +477,9 @@
 	fmt.Fprintf(w, "Pending peers: %d\n", len(t.peers))
 	fmt.Fprintf(w, "Half open: %d\n", len(t.halfOpen))
 	fmt.Fprintf(w, "Active peers: %d\n", len(t.conns))
-	slices.Sort(t.conns, worseConn)
-	for i, c := range t.conns {
+	conns := t.connsAsSlice()
+	slices.Sort(conns, worseConn)
+	for i, c := range conns {
 		fmt.Fprintf(w, "%2d. ", i+1)
 		c.WriteStatus(w, t)
 	}
@@ -558,7 +559,7 @@ 	t.closed.Set()
 	if t.storage != nil {
 		t.storage.Close()
 	}
-	for _, conn := range t.conns {
+	for conn := range t.conns {
 		conn.Close()
 	}
 	t.pieceStateChanges.Close()
@@ -873,7 +874,7 @@ 	t.openNewConns()
 }
 
 func (t *Torrent) piecePriorityChanged(piece int) {
-	for _, c := range t.conns {
+	for c := range t.conns {
 		c.updatePiecePriority(piece)
 	}
 	t.maybeNewConns()
@@ -1004,13 +1005,12 @@ 	ci := chunkIndex(req.chunkSpec, t.chunkSize)
 	t.pieces[req.Index].pendChunkIndex(ci)
 }
 
-func (t *Torrent) pieceChanged(piece int) {
-	correct := t.pieceComplete(piece)
-	defer t.cl.event.Broadcast()
-	if correct {
-		t.onCompletedPiece(piece)
+func (t *Torrent) pieceCompletionChanged(piece int) {
+	t.cl.event.Broadcast()
+	if t.pieceComplete(piece) {
+		t.onPieceCompleted(piece)
 	} else {
-		t.onFailedPiece(piece)
+		t.onIncompletePiece(piece)
 	}
 	t.updatePiecePriority(piece)
 }
@@ -1039,7 +1039,7 @@ 	pcu := t.pieceCompleteUncached(piece)
 	changed := t.completedPieces.Get(piece) != pcu
 	t.completedPieces.Set(piece, pcu)
 	if changed {
-		t.pieceChanged(piece)
+		t.pieceCompletionChanged(piece)
 	}
 }
 
@@ -1160,19 +1160,10 @@ 	return t.setInfoBytes(b)
 }
 
 // Returns true if connection is removed from torrent.Conns.
-func (t *Torrent) deleteConnection(c *connection) bool {
-	for i0, _c := range t.conns {
-		if _c != c {
-			continue
-		}
-		i1 := len(t.conns) - 1
-		if i0 != i1 {
-			t.conns[i0] = t.conns[i1]
-		}
-		t.conns = t.conns[:i1]
-		return true
-	}
-	return false
+func (t *Torrent) deleteConnection(c *connection) (ret bool) {
+	_, ret = t.conns[c]
+	delete(t.conns, c)
+	return
 }
 
 func (t *Torrent) dropConnection(c *connection) {
@@ -1356,7 +1347,7 @@ 	}
 	if !t.wantConns() {
 		return false
 	}
-	for _, c0 := range t.conns {
+	for c0 := range t.conns {
 		if c.PeerID == c0.PeerID {
 			// Already connected to a client with that ID.
 			duplicateClientConns.Add(1)
@@ -1377,7 +1368,6 @@ 	}
 	if len(t.conns) >= t.maxEstablishedConns {
 		panic(len(t.conns))
 	}
-	t.conns = append(t.conns, c)
 	if c.t != nil {
 		panic("connection already associated with a torrent")
 	}
@@ -1386,6 +1376,7 @@ 	// torrent.
 	t.stats.wroteBytes(c.stats.BytesWritten)
 	t.stats.readBytes(c.stats.BytesRead)
 	c.t = t
+	t.conns[c] = struct{}{}
 	return true
 }
 
@@ -1407,7 +1398,7 @@ 	t.cl.mu.Lock()
 	defer t.cl.mu.Unlock()
 	oldMax = t.maxEstablishedConns
 	t.maxEstablishedConns = max
-	wcs := slices.HeapInterface(append([]*connection(nil), t.conns...), worseConn)
+	wcs := slices.HeapInterface(slices.FromMapKeys(t.conns), worseConn)
 	for len(t.conns) > t.maxEstablishedConns && wcs.Len() > 0 {
 		t.dropConnection(wcs.Pop().(*connection))
 	}
@@ -1435,7 +1426,7 @@ 			pieceHashedNotCorrect.Add(1)
 		}
 	}
 	p.EverHashed = true
-	touchers := t.reapPieceTouches(piece)
+	touchers := t.reapPieceTouchers(piece)
 	if correct {
 		for _, c := range touchers {
 			c.goodPiecesDirtied++
@@ -1453,13 +1444,12 @@ 			t.cl.banPeerIP(missinggo.AddrIP(c.remoteAddr()))
 			t.dropConnection(c)
 		}
 	}
-	t.pieceChanged(piece)
 }
 
-func (t *Torrent) onCompletedPiece(piece int) {
+func (t *Torrent) onPieceCompleted(piece int) {
 	t.pendingPieces.Remove(piece)
 	t.pendAllChunkSpecs(piece)
-	for _, conn := range t.conns {
+	for conn := range t.conns {
 		conn.Have(piece)
 		for r := range conn.Requests {
 			if int(r.Index) == piece {
@@ -1472,16 +1462,14 @@ 		conn.upload()
 	}
 }
 
-func (t *Torrent) onFailedPiece(piece int) {
-	cl := t.cl
+func (t *Torrent) onIncompletePiece(piece int) {
 	if t.pieceAllDirty(piece) {
 		t.pendAllChunkSpecs(piece)
 	}
 	if !t.wantPieceIndex(piece) {
 		return
 	}
-	cl.openNewConns(t)
-	for _, conn := range t.conns {
+	for conn := range t.conns {
 		if conn.PeerHasPiece(piece) {
 			conn.updateRequests()
 		}
@@ -1512,8 +1500,8 @@ }
 
 // Return the connections that touched a piece, and clear the entry while
 // doing it.
-func (t *Torrent) reapPieceTouches(piece int) (ret []*connection) {
-	for _, c := range t.conns {
+func (t *Torrent) reapPieceTouchers(piece int) (ret []*connection) {
+	for c := range t.conns {
 		if _, ok := c.peerTouchedPieces[piece]; ok {
 			ret = append(ret, c)
 			delete(c.peerTouchedPieces, piece)
@@ -1521,3 +1509,10 @@ 		}
 	}
 	return
 }
+
+func (t *Torrent) connsAsSlice() (ret []*connection) {
+	for c := range t.conns {
+		ret = append(ret, c)
+	}
+	return
+}