diff --git a/doc/muxers.texi b/doc/muxers.texi
index 0972bbfd5c..0f8efabab9 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -1567,12 +1567,12 @@ It influences which tracks players should play by default. The default mode
 is @samp{infer}.
 @table @samp
 @item infer
-In this mode, for each type of track (audio, video or subtitle), if there is
-a track with disposition default of this type, then the first such track
-(i.e. the one with the lowest index) will be marked as default; if no such
-track exists, the first track of this type will be marked as default instead
-(if existing). This ensures that the default flag is set in a sensible way even
-if the input originated from containers that lack the concept of default tracks.
+Every track with disposition default will have the FlagDefault set.
+Additionally, for each type of track (audio, video or subtitle), if no track
+with disposition default of this type exists, then the first track of this type
+will be marked as default (if existing). This ensures that the default flag
+is set in a sensible way even if the input originated from containers that
+lack the concept of default tracks.
 @item infer_no_subs
 This mode is the same as infer except that if no subtitle track with
 disposition default exists, no subtitle track will be marked as default.
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 899a3388cd..e2d9159e2c 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -1395,7 +1395,8 @@ static int mkv_write_tracks(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;
     AVIOContext *pb = s->pb;
-    int i, ret, video_default_idx, audio_default_idx, subtitle_default_idx;
+    int video_default_idx = -1, audio_default_idx = -1, subtitle_default_idx = -1;
+    int i, ret;
 
     if (mkv->nb_attachments == s->nb_streams)
         return 0;
@@ -1405,11 +1406,7 @@ static int mkv_write_tracks(AVFormatContext *s)
         return ret;
 
     if (mkv->default_mode != DEFAULT_MODE_PASSTHROUGH) {
-        int video_idx, audio_idx, subtitle_idx;
-
-        video_idx    = video_default_idx    =
-        audio_idx    = audio_default_idx    =
-        subtitle_idx = subtitle_default_idx = -1;
+        int video_idx = -1, audio_idx = -1, subtitle_idx = -1;
 
         for (i = s->nb_streams - 1; i >= 0; i--) {
             AVStream *st = s->streams[i];
@@ -1435,8 +1432,7 @@ static int mkv_write_tracks(AVFormatContext *s)
     }
     for (i = 0; i < s->nb_streams; i++) {
         AVStream *st = s->streams[i];
-        int is_default = mkv->default_mode == DEFAULT_MODE_PASSTHROUGH ?
-                             st->disposition & AV_DISPOSITION_DEFAULT  :
+        int is_default = st->disposition & AV_DISPOSITION_DEFAULT ||
                              i == video_default_idx || i == audio_default_idx ||
                              i == subtitle_default_idx;
         ret = mkv_write_track(s, mkv, st, &mkv->tracks[i],
@@ -2823,8 +2819,8 @@ static const AVOption options[] = {
     { "flipped_raw_rgb", "Raw RGB bitmaps in VFW mode are stored bottom-up", OFFSET(flipped_raw_rgb), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
     { "write_crc32", "write a CRC32 element inside every Level 1 element", OFFSET(write_crc), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, FLAGS },
     { "default_mode", "Controls how a track's FlagDefault is inferred", OFFSET(default_mode), AV_OPT_TYPE_INT, { .i64 = DEFAULT_MODE_INFER }, DEFAULT_MODE_INFER, DEFAULT_MODE_PASSTHROUGH, FLAGS, "default_mode" },
-    { "infer", "For each track type, mark the first track of disposition default as default; if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER }, 0, 0, FLAGS, "default_mode" },
-    { "infer_no_subs", "For each track type, mark the first track of disposition default as default; for audio and video: if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER_NO_SUBS }, 0, 0, FLAGS, "default_mode" },
+    { "infer", "For each track type, mark each track of disposition default as default; if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER }, 0, 0, FLAGS, "default_mode" },
+    { "infer_no_subs", "For each track type, mark each track of disposition default as default; for audio and video: if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER_NO_SUBS }, 0, 0, FLAGS, "default_mode" },
     { "passthrough", "Use the disposition flag as-is", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_PASSTHROUGH }, 0, 0, FLAGS, "default_mode" },
     { NULL },
 };
diff --git a/tests/ref/fate/matroska-flac-extradata-update b/tests/ref/fate/matroska-flac-extradata-update
index fb17bfea0b..1a8add7736 100644
--- a/tests/ref/fate/matroska-flac-extradata-update
+++ b/tests/ref/fate/matroska-flac-extradata-update
@@ -1,5 +1,5 @@
-3c721898cf2cf3e2e6c43ad58952bd2d *tests/data/fate/matroska-flac-extradata-update.matroska
-2032 tests/data/fate/matroska-flac-extradata-update.matroska
+c2b76d47a9f0e9626a4999bd395cae08 *tests/data/fate/matroska-flac-extradata-update.matroska
+2029 tests/data/fate/matroska-flac-extradata-update.matroska
 #extradata 0:       34, 0x7acb09e7
 #extradata 1:       34, 0x7acb09e7
 #extradata 2:       34, 0x443402dd