diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index e3f8977..9d2e8b2 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -3475,7 +3475,11 @@
    parent.  If an error occurs :exc:`OSError` is raised.
 
    Note that some platforms including FreeBSD <= 6.3 and Cygwin have
-   known issues when using fork() from a thread.
+   known issues when using ``fork()`` from a thread.
+
+   .. versionchanged:: 3.8
+      Calling ``fork()`` in a subinterpreter is no longer supported
+      (:exc:`RuntimeError` is raised).
 
    .. warning::
 
@@ -3492,6 +3496,10 @@
    master end of the pseudo-terminal.  For a more portable approach, use the
    :mod:`pty` module.  If an error occurs :exc:`OSError` is raised.
 
+   .. versionchanged:: 3.8
+      Calling ``forkpty()`` in a subinterpreter is no longer supported
+      (:exc:`RuntimeError` is raised).
+
    .. availability:: some flavors of Unix.
 
 
diff --git a/Misc/NEWS.d/next/Documentation/2019-11-12-15-31-09.bpo-38778.PHhTlv.rst b/Misc/NEWS.d/next/Documentation/2019-11-12-15-31-09.bpo-38778.PHhTlv.rst
new file mode 100644
index 0000000..053e1d2
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2019-11-12-15-31-09.bpo-38778.PHhTlv.rst
@@ -0,0 +1 @@
+Document the fact that :exc:`RuntimeError` is raised if :meth:`os.fork` is called in a subinterpreter.