diff --git a/src/or/connection.c b/src/or/connection.c
index 919da19f59..4108aa2a23 100644
--- a/src/or/connection.c
+++ b/src/or/connection.c
@@ -481,6 +481,19 @@ void connection_send_cell(connection_t *conn) {
 
   /* ???? If we might not have added a cell above, why are we
    * ???? increasing outbuf_flushlen? -NM */
+  /* The connection_write_cell_to_buf() call doesn't increase the flushlen
+   * (if link padding is on). So if there isn't a whole cell waiting-but-
+   * not-yet-flushed, we add a padding cell. Thus in any case the gap between
+   * outbuf_datalen and outbuf_flushlen is at least sizeof(cell_t). -RD
+   */
+  /* XXXX actually, there are some subtle bugs lurking in here. They
+   * have to do with the fact that we don't handle connection failure
+   * cleanly. Sometimes we mark things to be closed later. Inside
+   * connection_write_cell_to_buf, it returns successfully without
+   * writing if the connection has been marked for close. We need to
+   * look at all our failure cases more carefully and make sure they do
+   * the right thing.
+   */
   conn->outbuf_flushlen += sizeof(cell_t); /* instruct it to send a cell */
   connection_start_writing(conn);