diff --git a/libavcodec/vp3.c b/libavcodec/vp3.c
index bdd4289a49..0340c22bb2 100644
--- a/libavcodec/vp3.c
+++ b/libavcodec/vp3.c
@@ -2339,6 +2339,8 @@ static av_cold int theora_decode_init(AVCodecContext *avctx)
     }
 
   for(i=0;i<3;i++) {
+    if (header_len[i] <= 0)
+        continue;
     init_get_bits(&gb, header_start[i], header_len[i] * 8);
 
     ptype = get_bits(&gb, 8);