diff --git a/libavcodec/vorbis_enc.c b/libavcodec/vorbis_enc.c
index 396ca4b829e21cb60bb71c5fe1e7edae194ad472..0cc974e3c8d6e59a2a605651c60625cf427fb8ed 100644
--- a/libavcodec/vorbis_enc.c
+++ b/libavcodec/vorbis_enc.c
@@ -915,6 +915,7 @@ static float * put_vector(codebook_t * book, PutBitContext * pb, float * num) {
     for (i = 0; i < book->nentries; i++) {
         float d = 0.;
         int j;
+        if (!book->entries[i].len) continue;
         for (j = 0; j < book->ndimentions; j++) {
             float a = (book->dimentions[i * book->ndimentions + j] - num[j]);
             d += a*a;