SF patch #474590 -- RISC OS support
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 4e23398..bb75e64 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -42,7 +42,7 @@
         t = int(time.time() % 1000000)
         pid = self._counter
         self._counter += 1
-        filename = "%s.%s.myhostname.mydomain" % (t, pid)
+        filename = os.extsep.join((str(t), str(pid), "myhostname", "mydomain"))
         tmpname = os.path.join(self._dir, "tmp", filename)
         newname = os.path.join(self._dir, dir, filename)
         fp = open(tmpname, "w")