use more robust quoting
diff --git a/Lib/test/test_popen.py b/Lib/test/test_popen.py
index 454ba17..95f6d20 100644
--- a/Lib/test/test_popen.py
+++ b/Lib/test/test_popen.py
@@ -17,7 +17,7 @@
 
 class PopenTest(unittest.TestCase):
     def _do_test_commandline(self, cmdline, expected):
-        cmd = '%r -c "import sys;print sys.argv" %s' % (python, cmdline)
+        cmd = '"%s" -c "import sys;print sys.argv" %s' % (python, cmdline)
         data = os.popen(cmd).read()
         got = eval(data)[1:] # strip off argv[0]
         self.assertEqual(got, expected)