diff --git a/libavcodec/hevc_mp4toannexb_bsf.c b/libavcodec/hevc_mp4toannexb_bsf.c
index 30f733d..477d86d 100644
--- a/libavcodec/hevc_mp4toannexb_bsf.c
+++ b/libavcodec/hevc_mp4toannexb_bsf.c
@@ -141,10 +141,14 @@
         int      nalu_type;
         int is_irap, add_extradata, extra_size, prev_size;
 
+        if (bytestream2_get_bytes_left(&gb) < s->length_size) {
+            ret = AVERROR_INVALIDDATA;
+            goto fail;
+        }
         for (i = 0; i < s->length_size; i++)
             nalu_size = (nalu_size << 8) | bytestream2_get_byte(&gb);
 
-        if (nalu_size < 2) {
+        if (nalu_size < 2 || nalu_size > bytestream2_get_bytes_left(&gb)) {
             ret = AVERROR_INVALIDDATA;
             goto fail;
         }