diff --git a/Lib/test/libregrtest/cmdline.py b/Lib/test/libregrtest/cmdline.py
index 9ba6ec63cad9f8..23ca3565662146 100644
--- a/Lib/test/libregrtest/cmdline.py
+++ b/Lib/test/libregrtest/cmdline.py
@@ -3,7 +3,7 @@
 import shlex
 import sys
 from test.support import os_helper
-from .utils import ALL_RESOURCES, RESOURCE_NAMES
+from .utils import ALL_RESOURCES, RESOURCE_NAMES, TestFilter
 
 
 USAGE = """\
@@ -161,7 +161,7 @@ def __init__(self, **kwargs) -> None:
         self.forever = False
         self.header = False
         self.failfast = False
-        self.match_tests = []
+        self.match_tests: TestFilter = []
         self.pgo = False
         self.pgo_extended = False
         self.worker_json = None
diff --git a/Lib/test/libregrtest/refleak.py b/Lib/test/libregrtest/refleak.py
index 59f48bd1e3cf78..8d18ff3ae96db5 100644
--- a/Lib/test/libregrtest/refleak.py
+++ b/Lib/test/libregrtest/refleak.py
@@ -52,7 +52,8 @@ def runtest_refleak(test_name, test_func,
     except ImportError:
         zdc = None # Run unmodified on platforms without zipimport support
     else:
-        zdc = zipimport._zip_directory_cache.copy()
+        # private attribute that mypy doesn't know about:
+        zdc = zipimport._zip_directory_cache.copy()  # type: ignore[attr-defined]
     abcs = {}
     for abc in [getattr(collections.abc, a) for a in collections.abc.__all__]:
         if not isabstract(abc):
diff --git a/Lib/test/libregrtest/results.py b/Lib/test/libregrtest/results.py
index ad1744899cadc0..477de777f2a9ad 100644
--- a/Lib/test/libregrtest/results.py
+++ b/Lib/test/libregrtest/results.py
@@ -33,7 +33,7 @@ def __init__(self):
         self.test_times: list[tuple[float, TestName]] = []
         self.stats = TestStats()
         # used by --junit-xml
-        self.testsuite_xml: list[str] = []
+        self.testsuite_xml: list = []
 
     def is_all_good(self):
         return (not self.bad
diff --git a/Lib/test/libregrtest/run_workers.py b/Lib/test/libregrtest/run_workers.py
index 25ca8623c687c5..7d2c1cd84cd1ee 100644
--- a/Lib/test/libregrtest/run_workers.py
+++ b/Lib/test/libregrtest/run_workers.py
@@ -10,7 +10,7 @@
 import threading
 import time
 import traceback
-from typing import Literal, TextIO
+from typing import Any, Literal, TextIO
 
 from test import support
 from test.support import os_helper, MS_WINDOWS
@@ -243,7 +243,9 @@ def create_json_file(self, stack: contextlib.ExitStack) -> tuple[JsonFile, TextI
 
             json_fd = json_tmpfile.fileno()
             if MS_WINDOWS:
-                json_handle = msvcrt.get_osfhandle(json_fd)
+                # The msvcrt module is only available on Windows;
+                # we run mypy with `--platform=linux` in CI
+                json_handle: int = msvcrt.get_osfhandle(json_fd)  # type: ignore[attr-defined]
                 json_file = JsonFile(json_handle,
                                      JsonFileType.WINDOWS_HANDLE)
             else:
@@ -257,7 +259,7 @@ def create_worker_runtests(self, test_name: TestName, json_file: JsonFile) -> Wo
         else:
             match_tests = None
 
-        kwargs = {}
+        kwargs: dict[str, Any] = {}
         if match_tests:
             kwargs['match_tests'] = [(test, True) for test in match_tests]
         if self.runtests.output_on_failure:
@@ -343,6 +345,7 @@ def _runtest(self, test_name: TestName) -> MultiprocessResult:
             json_file, json_tmpfile = self.create_json_file(stack)
             worker_runtests = self.create_worker_runtests(test_name, json_file)
 
+            retcode: str | int | None
             retcode, tmp_files = self.run_tmp_files(worker_runtests,
                                                     stdout_file.fileno())
 
diff --git a/Lib/test/libregrtest/runtests.py b/Lib/test/libregrtest/runtests.py
index 283c104c1afb37..4bf2b1fb576e04 100644
--- a/Lib/test/libregrtest/runtests.py
+++ b/Lib/test/libregrtest/runtests.py
@@ -33,7 +33,8 @@ def configure_subprocess(self, popen_kwargs: dict) -> None:
                 popen_kwargs['pass_fds'] = [self.file]
             case JsonFileType.WINDOWS_HANDLE:
                 # Windows handle
-                startupinfo = subprocess.STARTUPINFO()
+                # We run mypy with `--platform=linux` so it complains about this:
+                startupinfo = subprocess.STARTUPINFO()  # type: ignore[attr-defined]
                 startupinfo.lpAttributeList = {"handle_list": [self.file]}
                 popen_kwargs['startupinfo'] = startupinfo
 
diff --git a/Lib/test/libregrtest/setup.py b/Lib/test/libregrtest/setup.py
index 97edba9f87d7f9..9e9741493e9a5b 100644
--- a/Lib/test/libregrtest/setup.py
+++ b/Lib/test/libregrtest/setup.py
@@ -124,7 +124,8 @@ def setup_tests(runtests: RunTests):
         support.LONG_TIMEOUT = min(support.LONG_TIMEOUT, timeout)
 
     if runtests.hunt_refleak:
-        unittest.BaseTestSuite._cleanup = False
+        # private attribute that mypy doesn't know about:
+        unittest.BaseTestSuite._cleanup = False  # type: ignore[attr-defined]
 
     if runtests.gc_threshold is not None:
         gc.set_threshold(runtests.gc_threshold)
diff --git a/Lib/test/libregrtest/utils.py b/Lib/test/libregrtest/utils.py
index 5eb2d72186b2e6..5a0271bcc17d80 100644
--- a/Lib/test/libregrtest/utils.py
+++ b/Lib/test/libregrtest/utils.py
@@ -12,7 +12,7 @@
 import sysconfig
 import tempfile
 import textwrap
-from collections.abc import Callable
+from collections.abc import Callable, Iterable
 
 from test import support
 from test.support import os_helper
@@ -551,7 +551,7 @@ def is_cross_compiled():
     return ('_PYTHON_HOST_PLATFORM' in os.environ)
 
 
-def format_resources(use_resources: tuple[str, ...]):
+def format_resources(use_resources: Iterable[str]):
     use_resources = set(use_resources)
     all_resources = set(ALL_RESOURCES)
 
@@ -591,7 +591,7 @@ def display_header(use_resources: tuple[str, ...],
     print("== Python build:", ' '.join(get_build_info()))
     print("== cwd:", os.getcwd())
 
-    cpu_count = os.cpu_count()
+    cpu_count: object = os.cpu_count()
     if cpu_count:
         affinity = process_cpu_count()
         if affinity and affinity != cpu_count: