diff --git a/libavcodec/hevc_mp4toannexb_bsf.c b/libavcodec/hevc_mp4toannexb_bsf.c
index baa93628ed..30f733d775 100644
--- a/libavcodec/hevc_mp4toannexb_bsf.c
+++ b/libavcodec/hevc_mp4toannexb_bsf.c
@@ -144,6 +144,11 @@ static int hevc_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *out)
         for (i = 0; i < s->length_size; i++)
             nalu_size = (nalu_size << 8) | bytestream2_get_byte(&gb);
 
+        if (nalu_size < 2) {
+            ret = AVERROR_INVALIDDATA;
+            goto fail;
+        }
+
         nalu_type = (bytestream2_peek_byte(&gb) >> 1) & 0x3f;
 
         /* prepend extradata to IRAP frames */