diff --git a/libavcodec/wavpackenc.c b/libavcodec/wavpackenc.c
index 005cf7c2e5..3631a0819f 100644
--- a/libavcodec/wavpackenc.c
+++ b/libavcodec/wavpackenc.c
@@ -2813,6 +2813,8 @@ static int wavpack_encode_block(WavPackEncodeContext *s,
     block_size = bytestream2_tell_p(&pb);
     AV_WL32(out + 4, block_size - 8);
 
+    av_assert0(put_bits_left(&s->pb) > 0);
+
     return block_size;
 }