diff --git a/lib/libsys/open.2 b/lib/libsys/open.2
--- a/lib/libsys/open.2
+++ b/lib/libsys/open.2
@@ -464,6 +464,14 @@
 .Xr fstatat 2
 and related syscalls.
 .Pp
+And in reverse, a file descriptor
+.Dv fd
+referencing vnode can be converted
+to the
+.Dv O_PATH
+type of descriptor by using the following call
+.Dl opath_fd = openat(fd, \[dq]\[dq], O_EMPTY_PATH | O_PATH);
+.Pp
 If successful,
 .Fn open
 returns a non-negative integer, termed a file descriptor.