diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index ad25404424e..b00496ca4f7 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -723,6 +723,8 @@ def test_add_and_close(self):
     def test_lock_conflict(self):
         # Fork off a subprocess that will lock the file for 2 seconds,
         # unlock it, and then exit.
+        if not hasattr(os, 'fork'):
+            return
         pid = os.fork()
         if pid == 0:
             # In the child, lock the mailbox.