diff --git a/Lib/distutils/tests/test_build_ext.py b/Lib/distutils/tests/test_build_ext.py
index f0580c1..c671483 100644
--- a/Lib/distutils/tests/test_build_ext.py
+++ b/Lib/distutils/tests/test_build_ext.py
@@ -359,6 +359,7 @@
         self.assertEquals(lastdir, 'bar')
 
     def test_ext_fullpath(self):
+        ext = sysconfig.get_config_vars()['SO']
         # building lxml.etree inplace
         #etree_c = os.path.join(self.tmp_dir, 'lxml.etree.c')
         #etree_ext = Extension('lxml.etree', [etree_c])
@@ -369,14 +370,14 @@
         cmd.distribution.package_dir = {'': 'src'}
         cmd.distribution.packages = ['lxml', 'lxml.html']
         curdir = os.getcwd()
-        wanted = os.path.join(curdir, 'src', 'lxml', 'etree.so')
+        wanted = os.path.join(curdir, 'src', 'lxml', 'etree' + ext)
         path = cmd.get_ext_fullpath('lxml.etree')
         self.assertEquals(wanted, path)
 
         # building lxml.etree not inplace
         cmd.inplace = 0
         cmd.build_lib = os.path.join(curdir, 'tmpdir')
-        wanted = os.path.join(curdir, 'tmpdir', 'lxml', 'etree.so')
+        wanted = os.path.join(curdir, 'tmpdir', 'lxml', 'etree' + ext)
         path = cmd.get_ext_fullpath('lxml.etree')
         self.assertEquals(wanted, path)
 
@@ -386,13 +387,13 @@
         cmd.distribution.packages = ['twisted', 'twisted.runner.portmap']
         path = cmd.get_ext_fullpath('twisted.runner.portmap')
         wanted = os.path.join(curdir, 'tmpdir', 'twisted', 'runner',
-                              'portmap.so')
+                              'portmap' + ext)
         self.assertEquals(wanted, path)
 
         # building twisted.runner.portmap inplace
         cmd.inplace = 1
         path = cmd.get_ext_fullpath('twisted.runner.portmap')
-        wanted = os.path.join(curdir, 'twisted', 'runner', 'portmap.so')
+        wanted = os.path.join(curdir, 'twisted', 'runner', 'portmap' + ext)
         self.assertEquals(wanted, path)
 
 def test_suite():
diff --git a/Misc/NEWS b/Misc/NEWS
index e650b33..e1dba94 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -866,6 +866,8 @@
 Library
 -------
 
+- Issue #6455: Fixed test_build_ext under win32. 
+
 - Issue #6413: Fixed the log level in distutils.dist for announce.
 
 - Issue #6403: Fixed package path usage in build_ext.