diff --git a/mypy.ini b/mypy.ini
index 42ade6537ee..90c8ff13e70 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,5 +1,6 @@
 [mypy]
 # CI should test for all versions, local development gets hints for oldest supported
+# Some upstream typeshed distutils stubs fixes are necessary before we can start testing on Python 3.12
 python_version = 3.8
 strict = False
 warn_unused_ignores = True
@@ -8,6 +9,7 @@ explicit_package_bases = True
 exclude = (?x)(
 	^build/
 	| ^.tox/
+	| ^.egg/
 	| ^pkg_resources/tests/data/my-test-package-source/setup.py$ # Duplicate module name
 	| ^.+?/(_vendor|extern)/ # Vendored
 	| ^setuptools/_distutils/ # Vendored
diff --git a/pkg_resources/__init__.py b/pkg_resources/__init__.py
index 163a5521d67..c2ba0476e51 100644
--- a/pkg_resources/__init__.py
+++ b/pkg_resources/__init__.py
@@ -3193,7 +3193,7 @@ def _find_adapter(registry, ob):
     for t in types:
         if t in registry:
             return registry[t]
-    # _find_adapter would previously return None, and immediatly be called.
+    # _find_adapter would previously return None, and immediately be called.
     # So we're raising a TypeError to keep backward compatibility if anyone depended on that behaviour.
     raise TypeError(f"Could not find adapter for {registry} and {ob}")
 
diff --git a/setup.cfg b/setup.cfg
index 4d1155e884d..c41b226e0cf 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -73,6 +73,7 @@ testing =
 	# for tools/finalize.py
 	jaraco.develop >= 7.21; python_version >= "3.9" and sys_platform != "cygwin"
 	pytest-home >= 0.5
+	mypy==1.9  # pin mypy version so a new version doesn't suddenly cause the CI to fail
 	# No Python 3.11 dependencies require tomli, but needed for type-checking since we import it directly
 	tomli
 	# No Python 3.12 dependencies require importlib_metadata, but needed for type-checking since we import it directly
diff --git a/setup.py b/setup.py
index 1a6074766a5..542edaea681 100755
--- a/setup.py
+++ b/setup.py
@@ -88,6 +88,6 @@ def _restore_install_lib(self):
 
 if __name__ == '__main__':
     # allow setup.py to run from another directory
-    # TODO: Use a proper conditonal statement here
+    # TODO: Use a proper conditional statement here
     here and os.chdir(here)  # type: ignore[func-returns-value]
     dist = setuptools.setup(**setup_params)
diff --git a/setuptools/_core_metadata.py b/setuptools/_core_metadata.py
index 4bf3c7c947c..5dd97c7719f 100644
--- a/setuptools/_core_metadata.py
+++ b/setuptools/_core_metadata.py
@@ -62,7 +62,7 @@ def _read_list_from_msg(msg: Message, field: str) -> Optional[List[str]]:
 
 
 def _read_payload_from_msg(msg: Message) -> Optional[str]:
-    value = msg.get_payload().strip()
+    value = str(msg.get_payload()).strip()
     if value == 'UNKNOWN' or not value:
         return None
     return value
diff --git a/setuptools/command/editable_wheel.py b/setuptools/command/editable_wheel.py
index 5f08ab53fca..4d21e2253fa 100644
--- a/setuptools/command/editable_wheel.py
+++ b/setuptools/command/editable_wheel.py
@@ -620,8 +620,7 @@ def _simple_layout(
     layout = {pkg: find_package_path(pkg, package_dir, project_dir) for pkg in packages}
     if not layout:
         return set(package_dir) in ({}, {""})
-    # TODO: has been fixed upstream, waiting for new mypy release https://github.com/python/typeshed/pull/11310
-    parent = os.path.commonpath(starmap(_parent_path, layout.items()))  # type: ignore[call-overload]
+    parent = os.path.commonpath(starmap(_parent_path, layout.items()))
     return all(
         _path.same_path(Path(parent, *key.split('.')), value)
         for key, value in layout.items()