diff --git a/libavcodec/dnxhddec.c b/libavcodec/dnxhddec.c
index 6e94d32ecc..0af685e28b 100644
--- a/libavcodec/dnxhddec.c
+++ b/libavcodec/dnxhddec.c
@@ -180,7 +180,7 @@ static int dnxhd_decode_header(DNXHDContext *ctx, const uint8_t *buf, int buf_si
     for (i = 0; i < ctx->mb_height; i++) {
         ctx->mb_scan_index[i] = AV_RB32(buf + 0x170 + (i<<2));
         av_dlog(ctx->avctx, "mb scan index %d\n", ctx->mb_scan_index[i]);
-        if (buf_size < ctx->mb_scan_index[i] + 0x280) {
+        if (buf_size < ctx->mb_scan_index[i] + 0x280LL) {
             av_log(ctx->avctx, AV_LOG_ERROR, "invalid mb scan index\n");
             return -1;
         }