diff --git a/src/wormhole/test/test_transit.py b/src/wormhole/test/test_transit.py
index e04d9f1..de9d6df 100644
--- a/src/wormhole/test/test_transit.py
+++ b/src/wormhole/test/test_transit.py
@@ -132,6 +132,8 @@ class Misc(unittest.TestCase):
         portno = transit.allocate_tcp_port()
         self.assertIsInstance(portno, int)
 
+UnknownHint = namedtuple("UnknownHint", ["stuff"])
+
 class Hints(unittest.TestCase):
     def test_endpoint_from_hint_obj(self):
         c = transit.Common("")
@@ -153,7 +155,6 @@ class Hints(unittest.TestCase):
                          ("tor_ep", "host2.onion", 1234))
         self.assertEqual(efho(transit.DirectTCPV1Hint("non-public", 1234)),
                          None)
-        UnknownHint = namedtuple("UnknownHint", ["stuff"])
         self.assertEqual(efho(UnknownHint("foo")), None)
 
     def test_comparable(self):
@@ -185,6 +186,37 @@ class Hints(unittest.TestCase):
                             "port": "not a number"}),
                          None) # invalid port
 
+    def test_parse_hint_argv(self):
+        def p(hint):
+            stderr = io.StringIO()
+            value = transit.parse_hint_argv(hint, stderr=stderr)
+            return value, stderr.getvalue()
+        h,stderr = p("tcp:host:1234")
+        self.assertEqual(h, transit.DirectTCPV1Hint("host", 1234))
+        self.assertEqual(stderr, "")
+
+        h,stderr = p("$!@#^")
+        self.assertEqual(h, None)
+        self.assertEqual(stderr, "unparseable hint '$!@#^'\n")
+
+        h,stderr = p("unknown:stuff")
+        self.assertEqual(h, None)
+        self.assertEqual(stderr,
+                         "unknown hint type 'unknown' in 'unknown:stuff'\n")
+
+        h,stderr = p("tcp:host:number")
+        self.assertEqual(h, None)
+        self.assertEqual(stderr,
+                         "unparseable TCP hint 'tcp:host:number'\n")
+
+    def test_describe_hint_obj(self):
+        d = transit.describe_hint_obj
+        self.assertEqual(d(transit.DirectTCPV1Hint("host", 1234)),
+                         "tcp:host:1234")
+        self.assertEqual(d(transit.TorTCPV1Hint("host", 1234)),
+                         "tor:host:1234")
+        self.assertEqual(d(UnknownHint("stuff")), str(UnknownHint("stuff")))
+
 class Basic(unittest.TestCase):
     @inlineCallbacks
     def test_relay_hints(self):
diff --git a/src/wormhole/transit.py b/src/wormhole/transit.py
index 3eb8272..284fb1b 100644
--- a/src/wormhole/transit.py
+++ b/src/wormhole/transit.py
@@ -103,27 +103,27 @@ def describe_hint_obj(hint):
     else:
         return str(hint)
 
-def parse_hint_argv(hint):
+def parse_hint_argv(hint, stderr=sys.stderr):
     assert isinstance(hint, type(u""))
     # return tuple or None for an unparseable hint
     mo = re.search(r'^([a-zA-Z0-9]+):(.*)$', hint)
     if not mo:
-        print("unparseable hint '%s'" % (hint,))
+        print("unparseable hint '%s'" % (hint,), file=stderr)
         return None
     hint_type = mo.group(1)
     if hint_type != "tcp":
-        print("unknown hint type '%s' in '%s'" % (hint_type, hint))
+        print("unknown hint type '%s' in '%s'" % (hint_type, hint), file=stderr)
         return None
     hint_value = mo.group(2)
     mo = re.search(r'^(.*):(\d+)$', hint_value)
     if not mo:
-        print("unparseable TCP hint '%s'" % (hint,))
+        print("unparseable TCP hint '%s'" % (hint,), file=stderr)
         return None
     hint_host = mo.group(1)
     try:
         hint_port = int(mo.group(2))
     except ValueError:
-        print("non-numeric port in TCP hint '%s'" % (hint,))
+        print("non-numeric port in TCP hint '%s'" % (hint,), file=stderr)
         return None
     return DirectTCPV1Hint(hint_host, hint_port)