diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index b04a46be33..c7210f026b 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -905,7 +905,8 @@ fail:
 
 static int read_gab2_sub(AVStream *st, AVPacket *pkt)
 {
-    if (pkt->data && !strcmp(pkt->data, "GAB2") && AV_RL16(pkt->data + 5) == 2) {
+    if (pkt->size >= 7 &&
+        !strcmp(pkt->data, "GAB2") && AV_RL16(pkt->data + 5) == 2) {
         uint8_t desc[256];
         int score      = AVPROBE_SCORE_EXTENSION, ret;
         AVIStream *ast = st->priv_data;