diff --git a/libavformat/asfdec.c b/libavformat/asfdec.c
index cdde5ae3e9..71f4e79fd5 100644
--- a/libavformat/asfdec.c
+++ b/libavformat/asfdec.c
@@ -235,7 +235,6 @@ static int asf_read_stream_properties(AVFormatContext *s, int64_t size)
     if (!asf_st)
         return AVERROR(ENOMEM);
     st->priv_data = asf_st;
-    st->start_time = 0;
     start_time = asf->hdr.preroll;
 
     asf_st->stream_language_index = 128; // invalid stream index means no language info
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 0471fd6c25..7990ce7bbe 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -534,6 +534,8 @@ typedef struct AVStream {
      * Only set this if you are absolutely 100% sure that the value you set
      * it to really is the pts of the first frame.
      * This may be undefined (AV_NOPTS_VALUE).
+     * @note The ASF header does NOT contain a correct start_time the ASF
+     * demuxer must NOT set this.
      */
     int64_t start_time;