diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
index b27ed5bd6d..858dca660c 100644
--- a/libavcodec/mpeg12dec.c
+++ b/libavcodec/mpeg12dec.c
@@ -1340,9 +1340,11 @@ static int mpeg1_decode_picture(AVCodecContext *avctx, const uint8_t *buf,
 {
     Mpeg1Context *s1  = avctx->priv_data;
     MpegEncContext *s = &s1->mpeg_enc_ctx;
-    int ref, f_code, vbv_delay;
+    int ref, f_code, vbv_delay, ret;
 
-    init_get_bits(&s->gb, buf, buf_size * 8);
+    ret = init_get_bits8(&s->gb, buf, buf_size);
+    if (ret < 0)
+        return ret;
 
     ref = get_bits(&s->gb, 10); /* temporal ref */
     s->pict_type = get_bits(&s->gb, 3);