diff -r 3a451c67008d Lib/test/libregrtest/cmdline.py
--- a/Lib/test/libregrtest/cmdline.py	Mon Dec 12 09:56:55 2016 +0100
+++ b/Lib/test/libregrtest/cmdline.py	Tue Dec 13 02:09:54 2016 +0800
@@ -301,9 +301,9 @@
 
     if ns.single and ns.fromfile:
         parser.error("-s and -f don't go together!")
-    if ns.use_mp and ns.trace:
+    if ns.use_mp is not None and ns.trace:
         parser.error("-T and -j don't go together!")
-    if ns.use_mp and ns.findleaks:
+    if ns.use_mp is not None and ns.findleaks:
         parser.error("-l and -j don't go together!")
     if ns.failfast and not (ns.verbose or ns.verbose3):
         parser.error("-G/--failfast needs either -v or -W")