diff --git a/stb_vorbis.c b/stb_vorbis.c
index 4e67726..2662d15 100644
--- a/stb_vorbis.c
+++ b/stb_vorbis.c
@@ -1601,6 +1601,8 @@ static uint32 get_bits(vorb *f, int n)
       }
    }
 
+   assert(f->valid_bits >= n);
+   
    z = f->acc & ((1 << n)-1);
    f->acc >>= n;
    f->valid_bits -= n;