diff --git a/protocol/rtsp/rtsp.go b/protocol/rtsp/rtsp.go
index 22d84236..fb9130bc 100644
--- a/protocol/rtsp/rtsp.go
+++ b/protocol/rtsp/rtsp.go
@@ -132,8 +132,12 @@ func ReadResponse(r io.Reader) (*Response, error) {
 	}
 	s := scanner.Text()
 
-	if s[:5] != "RTSP/" || len(s) < minResponse {
-		return nil, errors.New("response not valid")
+	if len(s) < minResponse {
+		return nil, errors.New("response length too small")
+	}
+
+	if s[:5] != "RTSP/" {
+		return nil, errors.New("invalid response")
 	}
 	resp.Proto = "RTSP"