diff --git a/include/import/slz.h b/include/import/slz.h
index d7d486350..d01599ca4 100644
--- a/include/import/slz.h
+++ b/include/import/slz.h
@@ -152,7 +152,9 @@ static inline long slz_encode(struct slz_stream *strm, void *out,
  * possibly pending bits from the queue (up to 24 bits), rounding to the next
  * byte, then 4 bytes for the CRC when doing zlib/gzip, then another 4 bytes
  * for the input length for gzip. That may about to 4+4+4 = 12 bytes, that the
- * caller must ensure are available before calling the function.
+ * caller must ensure are available before calling the function. Note that if
+ * the initial header was never sent, it will be sent first as well (up to 10
+ * extra bytes).
  */
 static inline int slz_finish(struct slz_stream *strm, void *buf)
 {