diff --git a/mitogen/core.py b/mitogen/core.py
index 8428a479..c228079d 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -3623,7 +3623,7 @@ class ExternalContext(object):
         self.broker = Broker(activate_compat=False)
         self.router = Router(self.broker)
         self.router.debug = self.config.get('debug', False)
-        self.router.undirectional = self.config['unidirectional']
+        self.router.unidirectional = self.config['unidirectional']
         self.router.add_handler(
             fn=self._on_shutdown_msg,
             handle=SHUTDOWN,
diff --git a/tests/router_test.py b/tests/router_test.py
index 1bd6c26a..2b4a9d78 100644
--- a/tests/router_test.py
+++ b/tests/router_test.py
@@ -1,9 +1,11 @@
+import sys
 import time
 import zlib
 
 import unittest2
 
 import testlib
+import mitogen.core
 import mitogen.master
 import mitogen.parent
 import mitogen.utils
@@ -341,22 +343,42 @@ class NoRouteTest(testlib.RouterMixin, testlib.TestCase):
         ))
 
 
+def test_siblings_cant_talk(router):
+    l1 = router.local()
+    l2 = router.local()
+    logs = testlib.LogCapturer()
+    logs.start()
+
+    try:
+        l2.call(ping_context, l1)
+    except mitogen.core.CallError:
+        e = sys.exc_info()[1]
+
+    msg = mitogen.core.Router.unidirectional_msg % (
+        l2.context_id,
+        l1.context_id,
+    )
+    assert msg in str(e)
+    assert 'routing mode prevents forward of ' in logs.stop()
+
+
+@mitogen.core.takes_econtext
+def test_siblings_cant_talk_remote(econtext):
+    mitogen.parent.upgrade_router(econtext)
+    test_siblings_cant_talk(econtext.router)
+
+
 class UnidirectionalTest(testlib.RouterMixin, testlib.TestCase):
-    def test_siblings_cant_talk(self):
+    def test_siblings_cant_talk_master(self):
         self.router.unidirectional = True
-        l1 = self.router.local()
-        l2 = self.router.local()
-        logs = testlib.LogCapturer()
-        logs.start()
-        e = self.assertRaises(mitogen.core.CallError,
-                              lambda: l2.call(ping_context, l1))
+        test_siblings_cant_talk(self.router)
 
-        msg = self.router.unidirectional_msg % (
-            l2.context_id,
-            l1.context_id,
-        )
-        self.assertTrue(msg in str(e))
-        self.assertTrue('routing mode prevents forward of ' in logs.stop())
+    def test_siblings_cant_talk_parent(self):
+        # ensure 'unidirectional' attribute is respected for contexts started
+        # by children.
+        self.router.unidirectional = True
+        parent = self.router.local()
+        parent.call(test_siblings_cant_talk_remote)
 
     def test_auth_id_can_talk(self):
         self.router.unidirectional = True