diff --git a/AUTHORS b/AUTHORS
index 541de37..04b1a41 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -78,3 +78,4 @@ Thanks To
 * Eric Windisch, zmq getsockopt(EVENTS) wake correct threads (pull request 22)
 * Raymond Lu, fixing busy-wait in eventlet.green.ssl.socket.sendall()
 * Thomas Grainger, webcrawler example small fix, "requests" library import bug report
+* Peter Portante, save syscalls in socket.dup(), environ[REMOTE_PORT] in wsgi
diff --git a/eventlet/greenio.py b/eventlet/greenio.py
index b97266a..b6946e8 100644
--- a/eventlet/greenio.py
+++ b/eventlet/greenio.py
@@ -97,8 +97,10 @@ def set_nonblocking(fd):
                                       "(Windows pipes don't support non-blocking I/O)")
         # We managed to import fcntl.
         fileno = fd.fileno()
-        flags = fcntl.fcntl(fileno, fcntl.F_GETFL)
-        fcntl.fcntl(fileno, fcntl.F_SETFL, flags | os.O_NONBLOCK)
+        orig_flags = fcntl.fcntl(fileno, fcntl.F_GETFL)
+        new_flags = orig_flags | os.O_NONBLOCK
+        if new_flags != orig_flags:
+            fcntl.fcntl(fileno, fcntl.F_SETFL, new_flags)
     else:
         # socket supports setblocking()
         setblocking(0)
@@ -114,8 +116,13 @@ class GreenSocket(object):
     """
     Green version of socket.socket class, that is intended to be 100%
     API-compatible.
+
+    It also recognizes the keyword parameter, 'set_nonblocking=True'.
+    Pass False to indicate that socket is already in non-blocking mode
+    to save syscalls.
     """
     def __init__(self, family_or_realsock=socket.AF_INET, *args, **kwargs):
+        should_set_nonblocking = kwargs.pop('set_nonblocking', True)
         if isinstance(family_or_realsock, (int, long)):
             fd = _original_socket(family_or_realsock, *args, **kwargs)
         else:
@@ -129,7 +136,8 @@ class GreenSocket(object):
         except AttributeError:
             self._timeout = socket.getdefaulttimeout()
 
-        set_nonblocking(fd)
+        if should_set_nonblocking:
+            set_nonblocking(fd)
         self.fd = fd
         # when client calls setblocking(0) or settimeout(0) the socket must
         # act non-blocking
@@ -209,8 +217,7 @@ class GreenSocket(object):
 
     def dup(self, *args, **kw):
         sock = self.fd.dup(*args, **kw)
-        set_nonblocking(sock)
-        newsock = type(self)(sock)
+        newsock = type(self)(sock, set_nonblocking=False)
         newsock.settimeout(self.gettimeout())
         return newsock
 
diff --git a/tests/greenio_test.py b/tests/greenio_test.py
index 72c5529..c15ebd5 100644
--- a/tests/greenio_test.py
+++ b/tests/greenio_test.py
@@ -4,12 +4,13 @@ from eventlet import event, greenio, debug
 from eventlet.hubs import get_hub
 from eventlet.green import socket, time
 from eventlet.support import get_errno
-import errno
 
+import array
+import errno
 import eventlet
+import fcntl
 import os
 import sys
-import array
 import tempfile, shutil
 
 
@@ -551,6 +552,35 @@ class TestGreenSocket(LimitedTestCase):
         self.assertRaises(socket.timeout, client.recv, 1)
         server.wait()
 
+    def test_default_nonblocking(self):
+        sock1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        flags = fcntl.fcntl(sock1.fd.fileno(), fcntl.F_GETFL)
+        assert flags & os.O_NONBLOCK
+
+        sock2 = socket.socket(sock1.fd)
+        flags = fcntl.fcntl(sock2.fd.fileno(), fcntl.F_GETFL)
+        assert flags & os.O_NONBLOCK
+
+    def test_dup_nonblocking(self):
+        sock1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        flags = fcntl.fcntl(sock1.fd.fileno(), fcntl.F_GETFL)
+        assert flags & os.O_NONBLOCK
+
+        sock2 = sock1.dup()
+        flags = fcntl.fcntl(sock2.fd.fileno(), fcntl.F_GETFL)
+        assert flags & os.O_NONBLOCK
+
+    def test_skip_nonblocking(self):
+        sock1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        fd = sock1.fd.fileno()
+        flags = fcntl.fcntl(fd, fcntl.F_GETFL)
+        flags = fcntl.fcntl(fd, fcntl.F_SETFL, flags & ~os.O_NONBLOCK)
+        assert flags & os.O_NONBLOCK == 0
+
+        sock2 = socket.socket(sock1.fd, set_nonblocking=False)
+        flags = fcntl.fcntl(sock2.fd.fileno(), fcntl.F_GETFL)
+        assert flags & os.O_NONBLOCK == 0
+
 
 class TestGreenPipe(LimitedTestCase):
     @skip_on_windows
@@ -821,5 +851,16 @@ class TestGreenIoStarvation(LimitedTestCase):
         assert maxstartdiff * 2 < runlengths[0], "Largest difference in starting times more than twice the shortest running time!"
         assert runlengths[0] * 2 > runlengths[-1], "Longest runtime more than twice as long as shortest!"
 
+
+def test_set_nonblocking():
+    sock = _orig_sock.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    fileno = sock.fileno()
+    orig_flags = fcntl.fcntl(fileno, fcntl.F_GETFL)
+    assert orig_flags & os.O_NONBLOCK == 0
+    greenio.set_nonblocking(sock)
+    new_flags = fcntl.fcntl(fileno, fcntl.F_GETFL)
+    assert new_flags == (orig_flags | os.O_NONBLOCK)
+
+
 if __name__ == '__main__':
     main()