diff --git a/letsencrypt/client/standalone_authenticator.py b/letsencrypt/client/standalone_authenticator.py
index 4bd6d3379..ef926f0ea 100644
--- a/letsencrypt/client/standalone_authenticator.py
+++ b/letsencrypt/client/standalone_authenticator.py
@@ -272,15 +272,18 @@ class StandaloneAuthenticator(object):
         :param int port: The TCP port in question.
         :returns: True or False."""
 
-        listeners = [conn.pid for conn in psutil.net_connections() \
-                     if conn.status == 'LISTEN' and \
-                     conn.type == socket.SOCK_STREAM and \
-                     (conn.laddr == ('0.0.0.0', port) or \
-                     conn.laddr == ('::', port))]
+        listeners = [conn.pid for conn in psutil.net_connections()
+                     if conn.status == 'LISTEN' and
+                     conn.type == socket.SOCK_STREAM and
+                     (conn.laddr[1] == port)]
         try:
-            if listeners and listeners[0]:
+            if listeners and listeners[0] is not None:
                 # conn.pid may be None if the current process doesn't have
-                # permission to identify the listening process!
+                # permission to identify the listening process!  Additionally,
+                # listeners may have more than one element if separate
+                # sockets have bound the same port on separate interfaces.
+                # We currently only have UI to notify the user about one
+                # of them at a time.
                 pid = listeners[0]
                 name = psutil.Process(pid).name()
                 display = zope.component.getUtility(interfaces.IDisplay)
@@ -290,9 +293,11 @@ class StandaloneAuthenticator(object):
                     "that port. Please stop the {0} program temporarily "
                     "and then try again.".format(name, pid, port))
                 return True
-        except psutil.NoSuchProcess:
+        except (psutil.NoSuchProcess, psutil.AccessDenied):
             # Perhaps the result of a race where the process could have
-            # exited or relinquished the port.
+            # exited or relinquished the port (NoSuchProcess), or the result
+            # of an OS policy where we're not allowed to look up the process
+            # name (AccessDenied).
             pass
         return False
 
diff --git a/letsencrypt/client/tests/standalone_authenticator_test.py b/letsencrypt/client/tests/standalone_authenticator_test.py
index abe3ff42d..542915c7a 100644
--- a/letsencrypt/client/tests/standalone_authenticator_test.py
+++ b/letsencrypt/client/tests/standalone_authenticator_test.py
@@ -1,6 +1,7 @@
 """Tests for letsencrypt.client.standalone_authenticator."""
 import os
 import pkg_resources
+import psutil
 import signal
 import socket
 import unittest
@@ -197,7 +198,6 @@ class AlreadyListeningTest(unittest.TestCase):
         # incompatibility in which, for some reason, no process name can be
         # found to match the identified listening PID.
         from psutil._common import sconn
-        from psutil import NoSuchProcess
         conns = [
             sconn(fd=-1, family=2, type=1, laddr=('0.0.0.0', 30),
                   raddr=(), status='LISTEN', pid=None),
@@ -208,7 +208,7 @@ class AlreadyListeningTest(unittest.TestCase):
             sconn(fd=3, family=2, type=1, laddr=('0.0.0.0', 17),
                   raddr=(), status='LISTEN', pid=4416)]
         mock_net.return_value = conns
-        mock_process.side_effect = NoSuchProcess("No such PID")
+        mock_process.side_effect = psutil.NoSuchProcess("No such PID")
         # We simulate being unable to find the process name of PID 4416,
         # which results in returning False.
         self.assertFalse(self.authenticator.already_listening(17))
diff --git a/setup.py b/setup.py
index 1136202ff..d8243af8a 100755
--- a/setup.py
+++ b/setup.py
@@ -26,7 +26,7 @@ install_requires = [
     'ConfArgParse',
     'jsonschema',
     'mock',
-    'psutil',
+    'psutil>2.1.0',  # net_connections introduced in 2.1.0
     'pycrypto',
     'PyOpenSSL',
     'python-augeas',