diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
index 8ad906a480..42e437f5d1 100644
--- a/libavformat/hlsenc.c
+++ b/libavformat/hlsenc.c
@@ -308,7 +308,7 @@ static void write_codec_attr(AVStream *st, VariantStream *vs) {
 
     if (st->codecpar->codec_id == AV_CODEC_ID_H264) {
         uint8_t *data = st->codecpar->extradata;
-        if ((data[0] | data[1] | data[2]) == 0 && data[3] == 1 && (data[4] & 0x1F) == 7) {
+        if (data && (data[0] | data[1] | data[2]) == 0 && data[3] == 1 && (data[4] & 0x1F) == 7) {
             snprintf(attr, sizeof(attr),
                      "avc1.%02x%02x%02x", data[5], data[6], data[7]);
         } else {