diff --git a/config/muxer.go b/config/muxer.go
index 6a48cb3bd412f00ae775ca0191e1db1fe1e78f60..ee2adeb08a2cb2ff2bfe7a737aa9c65ef57d74ec 100644
--- a/config/muxer.go
+++ b/config/muxer.go
@@ -50,6 +50,7 @@ func makeMuxer(h host.Host, tpts []MsMuxC) (mux.Transport, error) {
 		if _, ok := transportSet[tptC.ID]; ok {
 			return nil, fmt.Errorf("duplicate muxer transport: %s", tptC.ID)
 		}
+		transportSet[tptC.ID] = struct{}{}
 	}
 	for _, tptC := range tpts {
 		tpt, err := tptC.MuxC(h)