diff --git a/libavcodec/vc1dec.c b/libavcodec/vc1dec.c
index 5f1a5bd437..2c314e7b55 100644
--- a/libavcodec/vc1dec.c
+++ b/libavcodec/vc1dec.c
@@ -788,6 +788,7 @@ static av_cold void vc1_decode_reset(AVCodecContext *avctx)
     for (i = 0; i < 4; i++)
         av_freep(&v->sr_rows[i >> 1][i & 1]);
     ff_mpv_common_end(&v->s);
+    memset(v->s.block_index, 0, sizeof(v->s.block_index));
     av_freep(&v->mv_type_mb_plane);
     av_freep(&v->direct_mb_plane);
     av_freep(&v->forward_mb_plane);