diff --git a/libavformat/ffmetadec.c b/libavformat/ffmetadec.c
index bfda7d0bd8..69c93e6b3b 100644
--- a/libavformat/ffmetadec.c
+++ b/libavformat/ffmetadec.c
@@ -182,7 +182,7 @@ static int read_header(AVFormatContext *s)
     while(!avio_feof(s->pb)) {
         get_bprint_line(s->pb, &bp);
 
-        if (!memcmp(bp.str, ID_STREAM, strlen(ID_STREAM))) {
+        if (bp.len == strlen(ID_STREAM) && !memcmp(bp.str, ID_STREAM, strlen(ID_STREAM))) {
             AVStream *st = avformat_new_stream(s, NULL);
 
             if (!st)
@@ -192,7 +192,7 @@ static int read_header(AVFormatContext *s)
             st->codecpar->codec_id   = AV_CODEC_ID_FFMETADATA;
 
             m = &st->metadata;
-        } else if (!memcmp(bp.str, ID_CHAPTER, strlen(ID_CHAPTER))) {
+        } else if (bp.len == strlen(ID_CHAPTER) && !memcmp(bp.str, ID_CHAPTER, strlen(ID_CHAPTER))) {
             AVChapter *ch = read_chapter(s);
 
             if (!ch)