diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
index c6fca89d83..19b93df839 100644
--- a/libavformat/rtsp.c
+++ b/libavformat/rtsp.c
@@ -1578,7 +1578,11 @@ int ff_rtsp_make_setup_request(AVFormatContext *s, const char *host, int port,
         else if (lower_transport == RTSP_LOWER_TRANSPORT_UDP_MULTICAST) {
             snprintf(transport, sizeof(transport) - 1,
                      "%s/UDP;multicast", trans_pref);
+        } else {
+            err = AVERROR(EINVAL);
+            goto fail; // transport would be uninitialized
         }
+
         if (s->oformat) {
             av_strlcat(transport, ";mode=record", sizeof(transport));
         } else if (rt->server_type == RTSP_SERVER_REAL ||