diff --git a/src/allmydata/scripts/tahoe_daemonize.py b/src/allmydata/scripts/tahoe_daemonize.py
index 48fa16d56..40585fb26 100644
--- a/src/allmydata/scripts/tahoe_daemonize.py
+++ b/src/allmydata/scripts/tahoe_daemonize.py
@@ -115,6 +115,7 @@ class DaemonizeTheRealService(Service, HookMixin):
     - 'running': triggered when startup has completed; it triggers
         with None of successful or a Failure otherwise.
     """
+    stderr = sys.stderr
 
     def __init__(self, nodetype, basedir, options):
         super(DaemonizeTheRealService, self).__init__()
@@ -145,10 +146,12 @@ class DaemonizeTheRealService(Service, HookMixin):
                 raise ValueError("unknown nodetype %s" % self.nodetype)
 
             def handle_config_error(fail):
-                fail.trap(UnknownConfigError)
-                self.stderr.write("\nConfiguration error:\n{}\n\n".format(fail.value))
+                if fail.check(UnknownConfigError):
+                    self.stderr.write("\nConfiguration error:\n{}\n\n".format(fail.value))
+                else:
+                    self.stderr.write("\nUnknown error\n")
+                    fail.printTraceback(self.stderr)
                 reactor.stop()
-                return
 
             d = service_factory()
 
diff --git a/src/allmydata/test/cli/test_daemonize.py b/src/allmydata/test/cli/test_daemonize.py
index 414061977..e9a6d1ca0 100644
--- a/src/allmydata/test/cli/test_daemonize.py
+++ b/src/allmydata/test/cli/test_daemonize.py
@@ -1,4 +1,7 @@
 import os
+from io import (
+    BytesIO,
+)
 from os.path import dirname, join
 from mock import patch, Mock
 from six.moves import StringIO
@@ -52,6 +55,7 @@ class Util(unittest.TestCase):
 
     def test_daemonize_no_keygen(self):
         tmpdir = self.mktemp()
+        stderr = BytesIO()
         plug = DaemonizeTahoeNodePlugin('key-generator', tmpdir)
 
         with patch('twisted.internet.reactor') as r:
@@ -59,8 +63,8 @@ class Util(unittest.TestCase):
                 d = fn()
                 d.addErrback(lambda _: None)  # ignore the error we'll trigger
             r.callWhenRunning = call
-            r.stop = 'foo'
             service = plug.makeService(self.options)
+            service.stderr = stderr
             service.parent = Mock()
             # we'll raise ValueError because there's no key-generator
             # .. BUT we do this in an async function called via
@@ -70,7 +74,7 @@ class Util(unittest.TestCase):
             def done(f):
                 self.assertIn(
                     "key-generator support removed",
-                    str(f),
+                    stderr.getvalue(),
                 )
                 return None
             d.addBoth(done)