diff --git a/libavcodec/dvdsub_parser.c b/libavcodec/dvdsub_parser.c
index 44738a73d6..8871b6a383 100644
--- a/libavcodec/dvdsub_parser.c
+++ b/libavcodec/dvdsub_parser.c
@@ -43,7 +43,7 @@ static int dvdsub_parse(AVCodecParserContext *s,
     *poutbuf_size = buf_size;
 
     if (pc->packet_index == 0) {
-        if (buf_size < 2 || AV_RB16(buf) && buf_size < 6) {
+        if (buf_size < 2 || (AV_RB16(buf) == 0 && buf_size < 6)) {
             if (buf_size)
                 av_log(avctx, AV_LOG_DEBUG, "Parser input %d too small\n", buf_size);
             return buf_size;