diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index 3e7fad8..bd583e8 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -3863,7 +3863,9 @@
   BIO *wbio; /* used by SSL_write */
 
   /* bbio, if non-NULL, is a buffer placed in front of |wbio| to pack handshake
-   * messages within one flight into a single |BIO_write|.
+   * messages within one flight into a single |BIO_write|. In this case, |wbio|
+   * and |bbio| are equal and the true caller-configured BIO is
+   * |bbio->next_bio|.
    *
    * TODO(davidben): This does not work right for DTLS. It assumes the MTU is
    * smaller than the buffer size so that the buffer's internal flushing never