diff --git a/doc/api/child_process.md b/doc/api/child_process.md
index 63229fe68362af..57656ecbfdde77 100644
--- a/doc/api/child_process.md
+++ b/doc/api/child_process.md
@@ -784,6 +784,9 @@ pipes between the parent and child. The value is one of the following:
    `child_process` object as [`subprocess.stdio[fd]`][`subprocess.stdio`]. Pipes
    created for fds 0, 1, and 2 are also available as [`subprocess.stdin`][],
    [`subprocess.stdout`][] and [`subprocess.stderr`][], respectively.
+   Currently, these are not actual Unix pipes and therefore the child process
+   can not use them by their descriptor files,
+   e.g. `/dev/fd/2` or `/dev/stdout`.
 2. `'overlapped'`: Same as `'pipe'` except that the `FILE_FLAG_OVERLAPPED` flag
    is set on the handle. This is necessary for overlapped I/O on the child
    process's stdio handles. See the