diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 78189f4..70d129b3 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1142,7 +1142,10 @@
                 errread, errwrite = self.pipe_cloexec()
                 to_close.update((errread, errwrite))
             elif stderr == STDOUT:
-                errwrite = c2pwrite
+                if c2pwrite is not None:
+                    errwrite = c2pwrite
+                else: # child's stdout is not set, use parent's stdout
+                    errwrite = sys.__stdout__.fileno()
             elif isinstance(stderr, int):
                 errwrite = stderr
             else: