diff --git a/libavcodec/hqx.c b/libavcodec/hqx.c
index c6f0989ee5..c28c274b24 100644
--- a/libavcodec/hqx.c
+++ b/libavcodec/hqx.c
@@ -150,7 +150,6 @@ static int decode_block(GetBitContext *gb, const VLCElem vlc[],
     int ac_idx;
     int run, lev, pos = 0;
 
-    memset(block, 0, 64 * sizeof(*block));
     dc = get_vlc2(gb, vlc, HQX_DC_VLC_BITS, 2);
     *last_dc += dc;
 
@@ -190,6 +189,8 @@ static int hqx_decode_422(HQXContext *ctx, int slice_no, int x, int y)
     int last_dc;
     int i, ret;
 
+    memset(slice->block, 0, sizeof(*slice->block) * 8);
+
     if (ctx->interlaced)
         flag = get_bits1(gb);
     else
@@ -271,6 +272,8 @@ static int hqx_decode_444(HQXContext *ctx, int slice_no, int x, int y)
     int last_dc;
     int i, ret;
 
+    memset(slice->block, 0, sizeof(*slice->block) * 12);
+
     if (ctx->interlaced)
         flag = get_bits1(gb);
     else