diff --git a/tests/mypy_selftest.py b/tests/mypy_selftest.py
index 4ee98f72bde3..edc158732f2c 100755
--- a/tests/mypy_selftest.py
+++ b/tests/mypy_selftest.py
@@ -19,7 +19,7 @@
         shutil.copytree('stdlib', str(dirpath / 'mypy/typeshed/stdlib'))
         shutil.copytree('third_party', str(dirpath / 'mypy/typeshed/third_party'))
         try:
-            subprocess.run(['./runtests.py'], cwd=str(dirpath / 'mypy'), check=True)
+            subprocess.run(['./runtests.py', '-j12'], cwd=str(dirpath / 'mypy'), check=True)
         except subprocess.CalledProcessError as e:
             print('mypy tests failed', file=sys.stderr)
             sys.exit(e.returncode)