diff --git a/Doc/lib/libsocket.tex b/Doc/lib/libsocket.tex
index 9ff5f01..f78ad2f 100644
--- a/Doc/lib/libsocket.tex
+++ b/Doc/lib/libsocket.tex
@@ -272,10 +272,16 @@
 omitted or zero.
 \end{funcdesc}
 
-\begin{funcdesc}{getservbyname}{servicename, protocolname}
+\begin{funcdesc}{getservbyname}{servicename\optional{, protocolname}}
 Translate an Internet service name and protocol name to a port number
-for that service.  The protocol name should be \code{'tcp'} or
-\code{'udp'}.
+for that service.  The optional protocol name, if given, should be
+\code{'tcp'} or \code{'udp'}, otherwise any protocol will match.
+\end{funcdesc}
+
+\begin{funcdesc}{getservbyport}{port\optional{, protocolname}}
+Translate an Internet port number and protocol name to a service name
+for that service.  The optional protocol name, if given, should be
+\code{'tcp'} or \code{'udp'}, otherwise any protocol will match.
 \end{funcdesc}
 
 \begin{funcdesc}{socket}{\optional{family\optional{,
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 6e2f80c..2831454 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -284,22 +284,34 @@
             self.assertEqual(swapped & mask, mask)
             self.assertRaises(OverflowError, func, 1L<<34)
 
-    def testGetServByName(self):
-        # Testing getservbyname()
-        # try a few protocols - not everyone has telnet enabled
-        for proto in ("telnet", "ssh", "www", "ftp"):
+    def testGetServBy(self):
+        eq = self.assertEqual
+        # Find one service that exists, then check all the related interfaces.
+        # I've ordered this by protocols that have both a tcp and udp
+        # protocol, at least for modern Linuxes.
+        for service in ('ssh', 'www', 'echo', 'imap2'):
             try:
-                socket.getservbyname(proto, 'tcp')
-                break
-            except socket.error:
-                pass
-            try:
-                socket.getservbyname(proto, 'udp')
+                port = socket.getservbyname(service, 'tcp')
                 break
             except socket.error:
                 pass
         else:
             raise socket.error
+        # Try same call with optional protocol omitted
+        port2 = socket.getservbyname(service)
+        eq(port, port2)
+        # Try udp, but don't barf it it doesn't exist
+        try:
+            udpport = socket.getservbyname(service, 'udp')
+        except socket.error:
+            udpport = None
+        else:
+            eq(udpport, port)
+        # Now make sure the lookup by port returns the same service name
+        eq(socket.getservbyport(port2), service)
+        eq(socket.getservbyport(port, 'tcp'), service)
+        if udpport is not None:
+            eq(socket.getservbyport(udpport, 'udp'), service)
 
     def testDefaultTimeout(self):
         # Testing default timeout
diff --git a/Misc/NEWS b/Misc/NEWS
index 41a79c8..138afe2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -231,6 +231,9 @@
 Extension modules
 -----------------
 
+- Added socket.getservbyport(), and make the second argument in
+  getservbyname() and getservbyport() optional.
+
 - time module code that deals with input POSIX timestamps will now raise
   ValueError if more than a second is lost in precision when the
   timestamp is cast to the platform C time_t type.  There's no chance
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 255e4df..46015f1 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -25,7 +25,8 @@
 - socket.gethostbyaddr(IP address) --> (hostname, [alias, ...], [IP addr, ...])
 - socket.gethostname() --> host name (string: 'spam' or 'spam.domain.com')
 - socket.getprotobyname(protocolname) --> protocol number
-- socket.getservbyname(servicename, protocolname) --> port number
+- socket.getservbyname(servicename[, protocolname]) --> port number
+- socket.getservbyport(portnumber[, protocolname]) --> service name
 - socket.socket([family[, type [, proto]]]) --> new socket object
 - socket.ntohs(16 bit value) --> new int object
 - socket.ntohl(32 bit value) --> new int object
@@ -2884,9 +2885,9 @@
 static PyObject *
 socket_getservbyname(PyObject *self, PyObject *args)
 {
-	char *name, *proto;
+	char *name, *proto=NULL;
 	struct servent *sp;
-	if (!PyArg_ParseTuple(args, "ss:getservbyname", &name, &proto))
+	if (!PyArg_ParseTuple(args, "s|s:getservbyname", &name, &proto))
 		return NULL;
 	Py_BEGIN_ALLOW_THREADS
 	sp = getservbyname(name, proto);
@@ -2899,12 +2900,43 @@
 }
 
 PyDoc_STRVAR(getservbyname_doc,
-"getservbyname(servicename, protocolname) -> integer\n\
+"getservbyname(servicename[, protocolname]) -> integer\n\
 \n\
 Return a port number from a service name and protocol name.\n\
-The protocol name should be 'tcp' or 'udp'.");
+The optional protocol name, if given, should be 'tcp' or 'udp',\n\
+otherwise any protocol will match.");
 
 
+/* Python interface to getservbyport(port).
+   This only returns the service name, since the other info is already
+   known or not useful (like the list of aliases). */
+
+/*ARGSUSED*/
+static PyObject *
+socket_getservbyport(PyObject *self, PyObject *args)
+{
+	int port;
+	char *proto=NULL;
+	struct servent *sp;
+	if (!PyArg_ParseTuple(args, "i|s:getservbyport", &port, &proto))
+		return NULL;
+	Py_BEGIN_ALLOW_THREADS
+	sp = getservbyport(htons(port), proto);
+	Py_END_ALLOW_THREADS
+	if (sp == NULL) {
+		PyErr_SetString(socket_error, "port/proto not found");
+		return NULL;
+	}
+	return PyString_FromString(sp->s_name);
+}
+
+PyDoc_STRVAR(getservbyport_doc,
+"getservbyport(port[, protocolname]) -> string\n\
+\n\
+Return the service name from a port number and protocol name.\n\
+The optional protocol name, if given, should be 'tcp' or 'udp',\n\
+otherwise any protocol will match.");
+
 /* Python interface to getprotobyname(name).
    This only returns the protocol number, since the other info is
    already known or not useful (like the list of aliases). */
@@ -3530,6 +3562,8 @@
 	 METH_VARARGS, gethostname_doc},
 	{"getservbyname",	socket_getservbyname,
 	 METH_VARARGS, getservbyname_doc},
+	{"getservbyport",	socket_getservbyport,
+	 METH_VARARGS, getservbyport_doc},
 	{"getprotobyname",	socket_getprotobyname,
 	 METH_VARARGS,getprotobyname_doc},
 #ifndef NO_DUP