diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
index 8d115fa040..1f44ed18d9 100644
--- a/libavcodec/h264dec.c
+++ b/libavcodec/h264dec.c
@@ -855,6 +855,8 @@ static int is_extra(const uint8_t *buf, int buf_size)
 {
     int cnt= buf[5]&0x1f;
     const uint8_t *p= buf+6;
+    if (!cnt)
+        return 0;
     while(cnt--){
         int nalsize= AV_RB16(p) + 2;
         if(nalsize > buf_size - (p-buf) || (p[2] & 0x9F) != 7)