diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index ac6e85f78c..11d086cbe8 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -749,8 +749,10 @@ static int avi_read_header(AVFormatContext *s, AVFormatParameters *ap)
     return 0;
 }
 
-static int read_gab2_sub(AVStream *st, AVPacket *pkt) {
-    if (!strcmp(pkt->data, "GAB2") && AV_RL16(pkt->data+5) == 2) {
+static int read_gab2_sub(AVStream *st, AVPacket *pkt)
+{
+    if (pkt->size >= 7 &&
+        !strcmp(pkt->data, "GAB2") && AV_RL16(pkt->data + 5) == 2) {
         uint8_t desc[256];
         int score = AVPROBE_SCORE_MAX / 2, ret;
         AVIStream *ast = st->priv_data;