diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index c223e549b74..14784fad663 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -1646,6 +1646,10 @@ written in Python, such as a mail server's external command delivery program.
 
    Fork a child process.  Return ``0`` in the child and the child's process id in the
    parent.  If an error occurs :exc:`OSError` is raised.
+
+   Note that some platforms including FreeBSD <= 6.3, Cygwin and OS/2 EMX have
+   known issues when using fork() from a thread.
+
    Availability: Unix.
 
 
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 4e8743700e6..c8f9cac8f9c 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -380,6 +380,12 @@ class ThreadJoinOnShutdown(unittest.TestCase):
         import os
         if not hasattr(os, 'fork'):
             return
+        # Skip platforms with known problems forking from a worker thread.
+        # See http://bugs.python.org/issue3863.
+        if sys.platform in ('freebsd4', 'freebsd5', 'freebsd6', 'os2emx'):
+            print >>sys.stderr, ('Skipping test_3_join_in_forked_from_thread'
+                                 ' due to known OS bugs on'), sys.platform
+            return
         script = """if 1:
             main_thread = threading.current_thread()
             def worker():
diff --git a/Misc/NEWS b/Misc/NEWS
index 1b08d76bd96..6e6c58d0f21 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -37,6 +37,9 @@ Library
 
 - Issue #3879: A regression in urllib.getproxies_enviroment was fixed.
 
+- Issue #3863: Disabled a unit test of fork being called from a thread
+  when running on platforms known to exhibit OS bugs when attempting that.
+
 Build
 -----