diff -r 5fae31006724 -r b744517b90bc Doc/library/os.rst
--- a/Doc/library/os.rst	Tue Feb 26 12:39:57 2013 +0000
+++ b/Doc/library/os.rst	Tue Feb 26 08:44:41 2013 -0500
@@ -1440,9 +1440,11 @@
    *target_is_directory*, which defaults to ``False``.
 
    On Windows, a symlink represents a file or a directory, and does not morph to
-   the target dynamically.  If *target_is_directory* is set to ``True``, the
-   symlink will be created as a directory symlink, otherwise as a file symlink
-   (the default).
+   the target dynamically.  For this reason, when creating a symlink on Windows,
+   if the target is not already present, the symlink will default to being a
+   file symlink.  If *target_is_directory* is set to ``True``, the symlink will
+   be created as a directory symlink.  This parameter is ignored if the target
+   exists (and the symlink is created with the same type as the target).
 
    Symbolic link support was introduced in Windows 6.0 (Vista).  :func:`symlink`
    will raise a :exc:`NotImplementedError` on Windows versions earlier than 6.0.
@@ -1455,6 +1457,7 @@
       administrator level. Either obtaining the privilege or running your
       application as an administrator are ways to successfully create symlinks.
 
+
       :exc:`OSError` is raised when the function is called by an unprivileged
       user.
 
diff -r 5fae31006724 -r b744517b90bc Lib/test/test_os.py
--- a/Lib/test/test_os.py	Tue Feb 26 12:39:57 2013 +0000
+++ b/Lib/test/test_os.py	Tue Feb 26 08:44:41 2013 -0500
@@ -478,12 +478,7 @@
             f.write("I'm " + path + " and proud of it.  Blame test_os.\n")
             f.close()
         if support.can_symlink():
-            if os.name == 'nt':
-                def symlink_to_dir(src, dest):
-                    os.symlink(src, dest, True)
-            else:
-                symlink_to_dir = os.symlink
-            symlink_to_dir(os.path.abspath(t2_path), link_path)
+            os.symlink(os.path.abspath(t2_path), link_path)
             sub2_tree = (sub2_path, ["link"], ["tmp3"])
         else:
             sub2_tree = (sub2_path, [], ["tmp3"])
@@ -1220,7 +1215,7 @@
             os.remove(self.missing_link)
 
     def test_directory_link(self):
-        os.symlink(self.dirlink_target, self.dirlink, True)
+        os.symlink(self.dirlink_target, self.dirlink)
         self.assertTrue(os.path.exists(self.dirlink))
         self.assertTrue(os.path.isdir(self.dirlink))
         self.assertTrue(os.path.islink(self.dirlink))
@@ -1312,6 +1307,38 @@
             shutil.rmtree(level1)
 
 
+@support.skip_unless_symlink
+class NonLocalSymlinkTests(unittest.TestCase):
+
+    def setUp(self):
+        """
+        Create this structure:
+
+        base
+         \___ some_dir
+        """
+        os.makedirs('base/some_dir')
+
+    def tearDown(self):
+        shutil.rmtree('base')
+
+    def test_directory_link_nonlocal(self):
+        """
+        The symlink target should resolve relative to the link, not relative
+        to the current directory.
+
+        Then, link base/some_link -> base/some_dir and ensure that some_link
+        is resolved as a directory.
+
+        In issue13772, it was discovered that directory detection failed if
+        the symlink target was not specified relative to the current
+        directory, which was a defect in the implementation.
+        """
+        src = os.path.join('base', 'some_link')
+        os.symlink('some_dir', src)
+        assert os.path.isdir(src)
+
+
 class FSEncodingTests(unittest.TestCase):
     def test_nop(self):
         self.assertEqual(os.fsencode(b'abc\xff'), b'abc\xff')
@@ -1364,6 +1391,7 @@
         Pep383Tests,
         Win32KillTests,
         Win32SymlinkTests,
+        NonLocalSymlinkTests,
         FSEncodingTests,
         PidTests,
         LoginTests,
diff -r 5fae31006724 -r b744517b90bc Modules/posixmodule.c
--- a/Modules/posixmodule.c	Tue Feb 26 12:39:57 2013 +0000
+++ b/Modules/posixmodule.c	Tue Feb 26 08:44:41 2013 -0500
@@ -5411,6 +5411,47 @@
     return has_CreateSymbolicLinkW;
 }
 
+void _dirname(WCHAR *path) {
+    /* Remove the last portion of the path */
+
+    WCHAR *ptr;
+
+    /* walk the path from the end until a backslash is encountered */
+    for(ptr = path + wcslen(path); ptr != path; ptr--)
+    {
+        if(*ptr == *L"\\" || *ptr == *L"/") {
+            break;
+        }
+    }
+    *ptr = 0;
+}
+
+int _is_abs(WCHAR *path) {
+    /* Is this path absolute? */
+
+    return path[0] == L'\\' || path[0] == L'/' || path[1] == ':';
+
+}
+
+void _join(WCHAR *dest_path, const WCHAR *root, const WCHAR *rest) {
+    /* join root and rest with a backslash */
+    int root_len;
+
+    if(_is_abs(rest)) {
+        wcscpy(dest_path, rest);
+        return;
+    }
+
+    root_len = wcslen(root);
+
+    wcscpy(dest_path, root);
+    if(root_len) {
+        dest_path[root_len] = *L"\\";
+        root_len += 1;
+    }
+    wcscpy(dest_path+root_len, rest);
+}
+
 PyDoc_STRVAR(win_symlink__doc__,
 "symlink(src, dst, target_is_directory=False)\n\n\
 Create a symbolic link pointing to src named dst.\n\
@@ -5426,6 +5467,9 @@
     PyObject *src, *dest;
     int target_is_directory = 0;
     DWORD res;
+    WIN32_FILE_ATTRIBUTE_DATA src_info;
+    WCHAR dest_parent[MAX_PATH];
+    WCHAR src_resolved[MAX_PATH] = L"";
 
     if (!check_CreateSymbolicLinkW())
     {
@@ -5446,6 +5490,18 @@
         return NULL;
     }
 
+    /* if src is a directory, ensure target_is_directory==1 */
+    /* dest_parent = os.path.dirname(dest) */
+    wcscpy(dest_parent, PyUnicode_AsUnicode(dest));
+    _dirname(dest_parent);
+    /* src_resolved = os.path.join(dest_parent, src) */
+    _join(src_resolved, dest_parent, PyUnicode_AsUnicode(src));
+    if(GetFileAttributesExW(src_resolved, GetFileExInfoStandard, &src_info))
+    {
+        target_is_directory = target_is_directory ||
+            (src_info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY);
+    }
+
     Py_BEGIN_ALLOW_THREADS
     res = Py_CreateSymbolicLinkW(
         PyUnicode_AsUnicode(dest),