Index: Lib/subprocess.py
===================================================================
--- Lib/subprocess.py	(revision 85802)
+++ Lib/subprocess.py	(working copy)
@@ -357,6 +357,7 @@
 
 if mswindows:
     import threading
+    import warnings
     import msvcrt
     import _subprocess
     class STARTUPINFO:
@@ -856,6 +857,9 @@
                 args = '{} /c "{}"'.format (comspec, args)
                 if (_subprocess.GetVersion() >= 0x80000000 or
                         os.path.basename(comspec).lower() == "command.com"):
+                    warnings.warn(
+                        "Special support for COMMAND.COM will be removed",
+                        DeprecationWarning, 3)
                     # Win9x, or using command.com on NT. We need to
                     # use the w9xpopen intermediate program. For more
                     # information, see KB Q150956