diff --git a/libavcodec/vc1_block.c b/libavcodec/vc1_block.c
index 94184b0873..775e3c516b 100644
--- a/libavcodec/vc1_block.c
+++ b/libavcodec/vc1_block.c
@@ -526,7 +526,7 @@ static int vc1_decode_ac_coeff(VC1Context *v, int *last, int *skip,
         int escape = decode210(gb);
         if (escape != 2) {
             index = get_vlc2(gb, ff_vc1_ac_coeff_table[codingset].table, AC_VLC_BITS, 3);
-            if (index < 0)
+            if (index >= ff_vc1_ac_sizes[codingset] - 1U)
                 return AVERROR_INVALIDDATA;
             run   = vc1_index_decode_table[codingset][index][0];
             level = vc1_index_decode_table[codingset][index][1];