Index: Lib/distutils/tests/test_build_ext.py
===================================================================
--- Lib/distutils/tests/test_build_ext.py	(revision 64406)
+++ Lib/distutils/tests/test_build_ext.py	(working copy)
@@ -11,6 +11,10 @@
 import unittest
 from test import support
 
+def _get_source_filename():
+    (srcdir,) = sysconfig.get_config_vars('srcdir')
+    return os.path.join(srcdir, 'Modules', 'xxmodule.c')
+
 class BuildExtTestCase(unittest.TestCase):
     def setUp(self):
         # Create a simple test environment
@@ -18,10 +22,8 @@
         self.tmp_dir = tempfile.mkdtemp(prefix="pythontest_")
         self.sys_path = sys.path[:]
         sys.path.append(self.tmp_dir)
+        shutil.copy(_get_source_filename(), self.tmp_dir)
 
-        xx_c = os.path.join(sysconfig.project_base, 'Modules', 'xxmodule.c')
-        shutil.copy(xx_c, self.tmp_dir)
-
     def test_build_ext(self):
         xx_c = os.path.join(self.tmp_dir, 'xxmodule.c')
         xx_ext = Extension('xx', [xx_c])
@@ -66,9 +68,11 @@
         shutil.rmtree(self.tmp_dir, False if os.name != "nt" else True)
 
 def test_suite():
-    if not sysconfig.python_build:
+    src = _get_source_filename()
+    if not os.path.exists(src):
         if support.verbose:
-            print('test_build_ext: The test must be run in a python build dir')
+            print('test_build_ext: Cannot find source code (test'
+                   ' must run in python build dir)')
         return unittest.TestSuite()
     else: return unittest.makeSuite(BuildExtTestCase)