diff --git a/libavformat/mov.c b/libavformat/mov.c
index 2328b8f445..6e954dd444 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -3805,7 +3805,7 @@ static int mov_read_trak(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     st = avformat_new_stream(c->fc, NULL);
     if (!st) return AVERROR(ENOMEM);
-    st->id = c->fc->nb_streams;
+    st->id = -1;
     sc = av_mallocz(sizeof(MOVStreamContext));
     if (!sc) return AVERROR(ENOMEM);
 
@@ -4087,6 +4087,11 @@ static int mov_read_tkhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     st = c->fc->streams[c->fc->nb_streams-1];
     sc = st->priv_data;
 
+    // Each stream (trak) should have exactly 1 tkhd. This catches bad files and
+    // avoids corrupting AVStreams mapped to an earlier tkhd.
+    if (st->id != -1)
+        return AVERROR_INVALIDDATA;
+
     version = avio_r8(pb);
     flags = avio_rb24(pb);
     st->disposition |= (flags & MOV_TKHD_FLAG_ENABLED) ? AV_DISPOSITION_DEFAULT : 0;