Index: subprocess.py
===================================================================
--- subprocess.py	(revision 52849)
+++ subprocess.py	(working copy)
@@ -717,6 +717,8 @@
 
         def _make_inheritable(self, handle):
             """Return a duplicate of handle, which is inheritable"""
+            if handle is None:
+                handle = -1         # INVALID_HANDLE_VALUE
             return DuplicateHandle(GetCurrentProcess(), handle,
                                    GetCurrentProcess(), 0, 1,
                                    DUPLICATE_SAME_ACCESS)