diff --git a/Lib/test/libregrtest/cmdline.py b/Lib/test/libregrtest/cmdline.py
index 891b00c..d621f5f 100644
--- a/Lib/test/libregrtest/cmdline.py
+++ b/Lib/test/libregrtest/cmdline.py
@@ -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")
diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
old mode 100644
new mode 100755
diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py
index 52909d8..751df15 100644
--- a/Lib/test/test_regrtest.py
+++ b/Lib/test/test_regrtest.py
@@ -226,6 +226,8 @@
                 self.checkError([opt, 'foo'], 'invalid int value')
                 self.checkError([opt, '2', '-T'], "don't go together")
                 self.checkError([opt, '2', '-l'], "don't go together")
+                self.checkError([opt, '0', '-T'], "don't go together")
+                self.checkError([opt, '0', '-l'], "don't go together")
 
     def test_coverage(self):
         for opt in '-T', '--coverage':