diff --git a/pyproject.toml b/pyproject.toml
index 1a45df95..bdf4e6f4 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,14 +13,11 @@ source = [
 ]
 
 [tool.coverage.report]
-exclude_also = [
-    "assert False",
-]
+exclude_also = ["assert False"]
 show_missing = true
 
 [tool.mypy]
 warn_unused_configs = true
-follow_imports = "skip"
 strict = true
 
 [[tool.mypy.overrides]]
diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index 3119c4f0..e7ae772c 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -264,10 +264,10 @@ def to_cryptography_key(self) -> _Key:
 
         if self._only_public:
             der = dump_publickey(FILETYPE_ASN1, self)
-            return load_der_public_key(der)
+            return typing.cast(_Key, load_der_public_key(der))
         else:
             der = dump_privatekey(FILETYPE_ASN1, self)
-            return load_der_private_key(der, None)
+            return typing.cast(_Key, load_der_private_key(der, password=None))
 
     @classmethod
     def from_cryptography_key(cls, crypto_key: _Key) -> PKey:
diff --git a/tests/conftest.py b/tests/conftest.py
index 73ab7a68..26711da7 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -7,13 +7,14 @@
 import pytest
 
 
-def pytest_report_header(config):
+def pytest_report_header(config: pytest.Config) -> str:
     import cryptography
 
     import OpenSSL.SSL
 
     return (
-        f"OpenSSL: {OpenSSL.SSL.SSLeay_version(OpenSSL.SSL.SSLEAY_VERSION)}\n"
+        f"OpenSSL: "
+        f"{OpenSSL.SSL.SSLeay_version(OpenSSL.SSL.SSLEAY_VERSION)!r}\n"
         f"cryptography: {cryptography.__version__}"
     )
 
diff --git a/tox.ini b/tox.ini
index 87842ff8..62b7ddfa 100644
--- a/tox.ini
+++ b/tox.ini
@@ -42,11 +42,12 @@ commands =
     ruff format --check .
 
 [testenv:py311-mypy]
+extras =
+    test
 deps =
     mypy
-skip_install = true
 commands =
-    mypy src
+    mypy src/ tests/conftest.py
 
 [testenv:check-manifest]
 deps =