diff --git a/demux/demux.c b/demux/demux.c
index 23ec713276..22b1a47ab1 100644
--- a/demux/demux.c
+++ b/demux/demux.c
@@ -933,6 +933,7 @@ void demuxer_feed_caption(struct sh_stream *stream, demux_packet_t *dp)
         return;
     }
 
+    dp->keyframe = true;
     dp->pts = MP_ADD_PTS(dp->pts, -in->ts_offset);
     dp->dts = MP_ADD_PTS(dp->dts, -in->ts_offset);
     pthread_mutex_unlock(&in->lock);