Index: Doc/library/os.rst
===================================================================
--- Doc/library/os.rst	(revision 80206)
+++ Doc/library/os.rst	(working copy)
@@ -879,10 +879,10 @@
    Unix.
 
 
-.. function:: listdir(path)
+.. function:: listdir([path])
 
    Return a list containing the names of the entries in the directory given by
-   *path*.  The list is in arbitrary order.  It does not include the special
+   *path* (default: '.').  The list is in arbitrary order.  It does not include the special
    entries ``'.'`` and ``'..'`` even if they are present in the directory.
    Availability: Unix, Windows.
 
Index: Lib/test/test_posix.py
===================================================================
--- Lib/test/test_posix.py	(revision 80206)
+++ Lib/test/test_posix.py	(working copy)
@@ -252,10 +252,15 @@
             posix.chdir(os.curdir)
             self.assertRaises(OSError, posix.chdir, support.TESTFN)
 
-    def test_lsdir(self):
-        if hasattr(posix, 'lsdir'):
-            self.assertIn(support.TESTFN, posix.lsdir(os.curdir))
+    def test_listdir(self):
+        if hasattr(posix, 'listdir'):
+            self.assertTrue(support.TESTFN in posix.listdir(os.curdir))
 
+    def test_listdir_default(self):
+        # When listdir is called without argument, it's the same as listdir(os.curdir)
+        if hasattr(posix, 'listdir'):
+            self.assertTrue(support.TESTFN in posix.listdir())
+
     def test_access(self):
         if hasattr(posix, 'access'):
             self.assertTrue(posix.access(support.TESTFN, os.R_OK))
Index: Modules/posixmodule.c
===================================================================
--- Modules/posixmodule.c	(revision 80206)
+++ Modules/posixmodule.c	(working copy)
@@ -2103,10 +2103,10 @@
 
 
 PyDoc_STRVAR(posix_listdir__doc__,
-"listdir(path) -> list_of_strings\n\n\
+"listdir([path]) -> list_of_strings\n\n\
 Return a list containing the names of the entries in the directory.\n\
 \n\
-	path: path of directory to list\n\
+	path: path of directory to list (default: '.')\n\
 \n\
 The list is in arbitrary order.  It does not include the special\n\
 entries '.' and '..' even if they are present in the directory.");
@@ -2127,18 +2127,25 @@
 	char *bufptr = namebuf;
 	Py_ssize_t len = sizeof(namebuf)-5; /* only claim to have space for MAX_PATH */
 
-	PyObject *po;
-	if (PyArg_ParseTuple(args, "U:listdir", &po)) {
+	PyObject *po = NULL;
+	if (PyArg_ParseTuple(args, "|U:listdir", &po)) {
 		WIN32_FIND_DATAW wFileData;
-		Py_UNICODE *wnamebuf;
+		Py_UNICODE *wnamebuf, *po_wchars;
+		
+		if (po == NULL) { // Default arg: "."
+			po_wchars = L".";
+			len = 1;
+		} else {
+			po_wchars = PyUnicode_AS_UNICODE(po);
+			len = PyUnicode_GET_SIZE(po);
+		}
 		/* Overallocate for \\*.*\0 */
-		len = PyUnicode_GET_SIZE(po);
 		wnamebuf = malloc((len + 5) * sizeof(wchar_t));
 		if (!wnamebuf) {
 			PyErr_NoMemory();
 			return NULL;
 		}
-		wcscpy(wnamebuf, PyUnicode_AS_UNICODE(po));
+		wcscpy(wnamebuf, po_wchars);
 		if (len > 0) {
 			Py_UNICODE wch = wnamebuf[len-1];
 			if (wch != L'/' && wch != L'\\' && wch != L':')
@@ -2360,12 +2367,16 @@
 	int arg_is_unicode = 1;
 
 	errno = 0;
-	if (!PyArg_ParseTuple(args, "U:listdir", &v)) {
+	if (!PyArg_ParseTuple(args, "|U:listdir", &v)) {
 		arg_is_unicode = 0;
 		PyErr_Clear();
 	}
-	if (!PyArg_ParseTuple(args, "O&:listdir", PyUnicode_FSConverter, &oname))
+	oname = NULL;
+	if (!PyArg_ParseTuple(args, "|O&:listdir", PyUnicode_FSConverter, &oname))
 		return NULL;
+	if (oname == NULL) { // Default arg: "."
+		oname = PyBytes_FromString(".");
+	}
 	name = bytes2str(oname, 1);
 	if ((dirp = opendir(name)) == NULL) {
 		return posix_error_with_allocated_filename(oname);