diff --git a/libavcodec/h264_cavlc.c b/libavcodec/h264_cavlc.c
index 0cc7214666..c01e94b5c1 100644
--- a/libavcodec/h264_cavlc.c
+++ b/libavcodec/h264_cavlc.c
@@ -770,6 +770,10 @@ decode_intra_mb:
 
         // We assume these blocks are very rare so we do not optimize it.
         align_get_bits(&s->gb);
+        if (get_bits_left(&s->gb) < mb_size) {
+            av_log(s->avctx, AV_LOG_ERROR, "Not enough data for an intra PCM block.\n");
+            return AVERROR_INVALIDDATA;
+        }
 
         // The pixels are stored in the same order as levels in h->mb array.
         for(x=0; x < mb_size; x++){