diff --git a/sysdep/unix/io.c b/sysdep/unix/io.c
index 13a2c8f8..cb57ffea 100644
--- a/sysdep/unix/io.c
+++ b/sysdep/unix/io.c
@@ -1415,6 +1415,10 @@ sk_ssh_connect(sock *s)
     switch (ssh_connect(s->ssh->session))
     {
     case SSH_AGAIN:
+      /* A quick look into libSSH shows that ssh_get_fd() should return non-(-1)
+       * after SSH_AGAIN is returned by ssh_connect(). This is however nowhere
+       * documented but our code relies on that.
+       */
       return SSH_AGAIN;
 
     case SSH_OK: