diff --git a/src/wormhole/_boss.py b/src/wormhole/_boss.py
index 2a1d2db..3b8950b 100644
--- a/src/wormhole/_boss.py
+++ b/src/wormhole/_boss.py
@@ -86,32 +86,38 @@ class Boss(object):
     def start(self):
         self._RC.start()
 
+    def _print_trace(self, old_state, input, new_state,
+                     client_name, machine, file):
+        if new_state:
+            print("%s.%s[%s].%s -> [%s]" %
+                  (client_name, machine, old_state, input,
+                   new_state), file=file)
+        else:
+            # the RendezvousConnector emits message events as if
+            # they were state transitions, except that old_state
+            # and new_state are empty strings. "input" is one of
+            # R.connected, R.rx(type phase+side), R.tx(type
+            # phase), R.lost .
+            print("%s.%s.%s" % (client_name, machine, input),
+                  file=file)
+        file.flush()
+        def output_tracer(output):
+            print(" %s.%s.%s()" % (client_name, machine, output),
+                  file=file)
+            file.flush()
+        return output_tracer
+
     def _set_trace(self, client_name, which, file):
         names = {"B": self, "N": self._N, "M": self._M, "S": self._S,
                  "O": self._O, "K": self._K, "SK": self._K._SK, "R": self._R,
                  "RC": self._RC, "L": self._L, "C": self._C,
                  "T": self._T}
         for machine in which.split():
-            def tracer(old_state, input, new_state, machine=machine):
-                if new_state:
-                    print("%s.%s[%s].%s -> [%s]" %
-                          (client_name, machine, old_state, input,
-                           new_state), file=file)
-                else:
-                    # the RendezvousConnector emits message events as if
-                    # they were state transitions, except that old_state
-                    # and new_state are empty strings. "input" is one of
-                    # R.connected, R.rx(type phase+side), R.tx(type
-                    # phase), R.lost .
-                    print("%s.%s.%s" % (client_name, machine, input),
-                          file=file)
-                file.flush()
-                def output_tracer(output):
-                    print(" %s.%s.%s()" % (client_name, machine, output),
-                          file=file)
-                    file.flush()
-                return output_tracer
-            names[machine].set_trace(tracer)
+            t = (lambda old_state, input, new_state:
+                 self._print_trace(old_state, input, new_state,
+                                   client_name=client_name,
+                                   machine=machine, file=file))
+            names[machine].set_trace(t)
 
     ## def serialize(self):
     ##     raise NotImplemented
diff --git a/src/wormhole/test/test_wormhole.py b/src/wormhole/test/test_wormhole.py
index 5b307d1..b42f6d3 100644
--- a/src/wormhole/test/test_wormhole.py
+++ b/src/wormhole/test/test_wormhole.py
@@ -527,3 +527,35 @@ class Reconnection(ServerBase, unittest.TestCase):
         self.assertEqual(c1, "happy")
         c2 = yield w2.close()
         self.assertEqual(c2, "happy")
+
+class Trace(unittest.TestCase):
+    def test_basic(self):
+        w1 = wormhole.create(APPID, "ws://localhost:1", reactor)
+        stderr = io.StringIO()
+        w1.debug_set_trace("W1", file=stderr)
+        # if Automat doesn't have the tracing API, then we won't actually
+        # exercise the tracing function, so exercise the RendezvousConnector
+        # function manually (it isn't a state machine, so it will always wire
+        # up the tracer)
+        w1._boss._RC._debug("what")
+
+        stderr = io.StringIO()
+        out = w1._boss._print_trace("OLD", "IN", "NEW", "C1", "M1", stderr)
+        self.assertEqual(stderr.getvalue().splitlines(),
+                         ["C1.M1[OLD].IN -> [NEW]"])
+        out("OUT1")
+        self.assertEqual(stderr.getvalue().splitlines(),
+                         ["C1.M1[OLD].IN -> [NEW]",
+                          " C1.M1.OUT1()"])
+        w1._boss._print_trace("", "R.connected", "", "C1", "RC1", stderr)
+        self.assertEqual(stderr.getvalue().splitlines(),
+                         ["C1.M1[OLD].IN -> [NEW]",
+                          " C1.M1.OUT1()",
+                          "C1.RC1.R.connected"])
+
+    def test_delegated(self):
+        dg = Delegate()
+        w1 = wormhole.create(APPID, "ws://localhost:1", reactor, delegate=dg)
+        stderr = io.StringIO()
+        w1.debug_set_trace("W1", file=stderr)
+        w1._boss._RC._debug("what")