config.go  |  1 +
 torrent.go | 14 ++++++++++++++

diff --git a/config.go b/config.go
index f438cbce8e93a27804d24c60f723836d506882b6..899a2f062f5deb55df1ccc95c76f9bec894bf9db 100644
--- a/config.go
+++ b/config.go
@@ -110,6 +110,7 @@ 	PublicIp4 net.IP
 	PublicIp6 net.IP
 
 	DisableAcceptRateLimiting bool
+	dropDuplicatePeerIds      bool
 }
 
 func (cfg *ClientConfig) SetListenAddr(addr string) *ClientConfig {
diff --git a/torrent.go b/torrent.go
index 62c61a10edcdf0a8afa9ffabe8b81adb1044a88f..3259dcc4d9db45ad542b1beab0a99612a03653b3 100644
--- a/torrent.go
+++ b/torrent.go
@@ -1503,6 +1503,20 @@ 	}()
 	if t.closed.IsSet() {
 		return errors.New("torrent closed")
 	}
+	for c0 := range t.conns {
+		if c.PeerID != c0.PeerID {
+			continue
+		}
+		if !t.cl.config.dropDuplicatePeerIds {
+			continue
+		}
+		if left, ok := c.hasPreferredNetworkOver(c0); ok && left {
+			c0.Close()
+			t.deleteConnection(c0)
+		} else {
+			return errors.New("existing connection preferred")
+		}
+	}
 	if !t.wantConns() {
 		return errors.New("don't want conns")
 	}