diff --git a/Lib/test/libregrtest/cmdline.py b/Lib/test/libregrtest/cmdline.py
index 2ff4715e82a41b..ced69da461bf83 100644
--- a/Lib/test/libregrtest/cmdline.py
+++ b/Lib/test/libregrtest/cmdline.py
@@ -157,7 +157,7 @@ def __init__(self, **kwargs) -> None:
         self.verbose3 = False
         self.print_slow = False
         self.random_seed = None
-        self.use_mp = None
+        self.use_mp = 0
         self.forever = False
         self.header = False
         self.failfast = False
diff --git a/Misc/NEWS.d/next/Tests/2024-06-13-17-11-54.gh-issue-119727.Fz2b2I.rst b/Misc/NEWS.d/next/Tests/2024-06-13-17-11-54.gh-issue-119727.Fz2b2I.rst
new file mode 100644
index 00000000000000..c96e9f235d228d
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2024-06-13-17-11-54.gh-issue-119727.Fz2b2I.rst
@@ -0,0 +1,3 @@
+The Python test runner (regrtest) now runs tests in parallel by default. Use
+the ``--single-process`` option to run tests sequentially in a single process.
+Patch by Victor Stinner.