diff --git a/demux/demux.c b/demux/demux.c
index 11b89a7b37..e09a4e843c 100644
--- a/demux/demux.c
+++ b/demux/demux.c
@@ -1245,6 +1245,7 @@ void demuxer_feed_caption(struct sh_stream *stream, demux_packet_t *dp)
     dp->keyframe = true;
     dp->pts = MP_ADD_PTS(dp->pts, -in->ts_offset);
     dp->dts = MP_ADD_PTS(dp->dts, -in->ts_offset);
+    dp->stream = sh->index;
     add_packet_locked(sh, dp);
     pthread_mutex_unlock(&in->lock);
 }
@@ -1892,6 +1893,10 @@ static void add_packet_locked(struct sh_stream *stream, demux_packet_t *dp)
         talloc_free(dp);
         return;
     }
+
+    assert(dp->stream == stream->index);
+    assert(!dp->next);
+
     struct demux_internal *in = ds->in;
 
     in->after_seek = false;
@@ -1945,9 +1950,6 @@ static void add_packet_locked(struct sh_stream *stream, demux_packet_t *dp)
     ds->global_correct_pos &= queue->correct_pos;
     ds->global_correct_dts &= queue->correct_dts;
 
-    dp->stream = stream->index;
-    dp->next = NULL;
-
     // (keep in mind that even if the reader went out of data, the queue is not
     // necessarily empty due to the backbuffer)
     if (!ds->reader_head && (!ds->skip_to_keyframe || dp->keyframe)) {