diff -r c43362d35d8d Lib/imaplib.py
--- a/Lib/imaplib.py	Fri Jul 04 17:00:25 2014 -0700
+++ b/Lib/imaplib.py	Tue Jul 08 20:58:47 2014 +0200
@@ -244,7 +244,9 @@
 
 
     def _create_socket(self):
-        return socket.create_connection((self.host, self.port))
+        # Workaround for issue 18540:
+        host = None if str(self.host) == '' else self.host
+        return socket.create_connection((host, self.port))
 
     def open(self, host = '', port = IMAP4_PORT):
         """Setup connection to remote server on "host:port"
diff -r c43362d35d8d Lib/test/test_imaplib.py
--- a/Lib/test/test_imaplib.py	Fri Jul 04 17:00:25 2014 -0700
+++ b/Lib/test/test_imaplib.py	Tue Jul 08 20:58:47 2014 +0200
@@ -228,6 +228,12 @@
             client.shutdown()
 
     @reap_threads
+    def test_issue18540(self):
+        # Test that the socket.connect method gets arguments plausible
+        # enough to attempt an connection.
+        self.assertRaises(ConnectionRefusedError, self.imap_class)
+
+    @reap_threads
     def test_issue5949(self):
 
         class EOFHandler(socketserver.StreamRequestHandler):