diff --git a/bin/make_dependency_update_pr.py b/bin/make_dependency_update_pr.py
index 62fb6f4af..54796641a 100755
--- a/bin/make_dependency_update_pr.py
+++ b/bin/make_dependency_update_pr.py
@@ -3,17 +3,17 @@
 from __future__ import annotations
 
 import os
+import subprocess
 import sys
 import textwrap
 import time
 from pathlib import Path
-from subprocess import run
 
 import click
 
 
-def shell(cmd, *, check: bool, **kwargs):
-    return run([cmd], shell=True, check=check, **kwargs)
+def shell(cmd: str, *, check: bool, **kwargs: object) -> subprocess.CompletedProcess[str]:
+    return subprocess.run([cmd], shell=True, check=check, **kwargs)  # type: ignore[call-overload, no-any-return]
 
 
 def git_repo_has_changes() -> bool:
@@ -59,7 +59,7 @@ def main() -> None:
             PR generated by `{os.path.basename(__file__)}`.
             """
         )
-        run(
+        subprocess.run(
             [
                 "gh",
                 "pr",
diff --git a/bin/projects.py b/bin/projects.py
index 3b39c3da4..09c5dc7f4 100755
--- a/bin/projects.py
+++ b/bin/projects.py
@@ -172,7 +172,9 @@ def get_projects(
     return sorted((Project(item, github) for item in config), reverse=online)
 
 
-def render_projects(projects: Sequence[Project], *, dest_path: Path, include_info: bool = True):
+def render_projects(
+    projects: Sequence[Project], *, dest_path: Path, include_info: bool = True
+) -> str:
     io = StringIO()
     print = functools.partial(builtins.print, file=io)
 
@@ -203,7 +205,7 @@ def insert_projects_table(
     projects: Sequence[Project],
     input_filename: str,
     include_info: bool = True,
-):
+) -> None:
     text = file.read_text()
     projects_table = render_projects(projects, include_info=include_info, dest_path=file)
 
diff --git a/bin/update_virtualenv.py b/bin/update_virtualenv.py
index fc69cf63d..b458c3f89 100755
--- a/bin/update_virtualenv.py
+++ b/bin/update_virtualenv.py
@@ -36,7 +36,7 @@ class VersionTuple:
     version_string: str
 
 
-def git_ls_remote_versions(url) -> list[VersionTuple]:
+def git_ls_remote_versions(url: str) -> list[VersionTuple]:
     versions: list[VersionTuple] = []
     tags = subprocess.run(
         ["git", "ls-remote", "--tags", url], check=True, text=True, capture_output=True
diff --git a/pyproject.toml b/pyproject.toml
index 9a9f3ecce..2dd8588f6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -115,7 +115,6 @@ warn_unused_configs = true
 
 strict = true
 disallow_untyped_defs = false
-disallow_incomplete_defs = false
 
 enable_error_code = ["ignore-without-code", "redundant-expr", "truthy-bool"]
 warn_unreachable = false
@@ -123,7 +122,6 @@ warn_unreachable = false
 [[tool.mypy.overrides]]
 module = "cibuildwheel.*"
 disallow_untyped_defs = true
-disallow_incomplete_defs = true
 
 [[tool.mypy.overrides]]
 module = [
diff --git a/test/conftest.py b/test/conftest.py
index e86c199d4..a42a3ce9a 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -11,7 +11,7 @@
 from .utils import EMULATED_ARCHS, platform
 
 
-def pytest_addoption(parser) -> None:
+def pytest_addoption(parser: pytest.Parser) -> None:
     parser.addoption(
         "--run-emulation",
         action="store",
diff --git a/test/test_testing.py b/test/test_testing.py
index b415fd403..a31dae514 100644
--- a/test/test_testing.py
+++ b/test/test_testing.py
@@ -155,7 +155,7 @@ def test_failing_test(tmp_path):
 @pytest.mark.parametrize("test_runner", ["pytest", "unittest"])
 def test_bare_pytest_invocation(
     tmp_path: Path, capfd: pytest.CaptureFixture[str], test_runner: str
-):
+) -> None:
     """Check that if a user runs pytest in the the test cwd, it raises a helpful error"""
     project_dir = tmp_path / "project"
     output_dir = tmp_path / "output"
diff --git a/unit_test/linux_build_steps_test.py b/unit_test/linux_build_steps_test.py
index ecf546ebd..ee608d0c7 100644
--- a/unit_test/linux_build_steps_test.py
+++ b/unit_test/linux_build_steps_test.py
@@ -4,12 +4,14 @@
 from pathlib import Path
 from pprint import pprint
 
+import pytest
+
 import cibuildwheel.linux
 from cibuildwheel.oci_container import OCIContainerEngineConfig
 from cibuildwheel.options import CommandLineArguments, Options
 
 
-def test_linux_container_split(tmp_path: Path, monkeypatch):
+def test_linux_container_split(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     """
     Tests splitting linux builds by container image, container engine, and before_all
     """
diff --git a/unit_test/oci_container_test.py b/unit_test/oci_container_test.py
index f43a3641c..11d991d11 100644
--- a/unit_test/oci_container_test.py
+++ b/unit_test/oci_container_test.py
@@ -239,7 +239,7 @@ def test_binary_output(container_engine):
         assert output == binary_data_string
 
 
-def test_file_operation(tmp_path: Path, container_engine):
+def test_file_operation(tmp_path: Path, container_engine: OCIContainerEngineConfig) -> None:
     with OCIContainer(
         engine=container_engine, image=DEFAULT_IMAGE, oci_platform=DEFAULT_OCI_PLATFORM
     ) as container:
@@ -259,7 +259,7 @@ def test_file_operation(tmp_path: Path, container_engine):
         assert test_binary_data == bytes(output, encoding="utf8", errors="surrogateescape")
 
 
-def test_dir_operations(tmp_path: Path, container_engine):
+def test_dir_operations(tmp_path: Path, container_engine: OCIContainerEngineConfig) -> None:
     with OCIContainer(
         engine=container_engine, image=DEFAULT_IMAGE, oci_platform=DEFAULT_OCI_PLATFORM
     ) as container:
@@ -301,7 +301,7 @@ def test_dir_operations(tmp_path: Path, container_engine):
         assert test_binary_data == (new_test_dir / "test.dat").read_bytes()
 
 
-def test_environment_executor(container_engine):
+def test_environment_executor(container_engine: OCIContainerEngineConfig) -> None:
     with OCIContainer(
         engine=container_engine, image=DEFAULT_IMAGE, oci_platform=DEFAULT_OCI_PLATFORM
     ) as container:
@@ -309,7 +309,9 @@ def test_environment_executor(container_engine):
         assert assignment.evaluated_value({}, container.environment_executor) == "42"
 
 
-def test_podman_vfs(tmp_path: Path, monkeypatch, container_engine):
+def test_podman_vfs(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, container_engine: OCIContainerEngineConfig
+) -> None:
     if container_engine.name != "podman":
         pytest.skip("only runs with podman")
     if sys.platform.startswith("darwin"):
@@ -391,7 +393,7 @@ def test_podman_vfs(tmp_path: Path, monkeypatch, container_engine):
     subprocess.run(["podman", "unshare", "rm", "-rf", vfs_path], check=True)
 
 
-def test_create_args_volume(tmp_path: Path, container_engine):
+def test_create_args_volume(tmp_path: Path, container_engine: OCIContainerEngineConfig) -> None:
     if container_engine.name != "docker":
         pytest.skip("only runs with docker")
 
@@ -513,7 +515,12 @@ def test_enforce_32_bit(container_engine):
         ("{name}; disable_host_mount: true", False),
     ],
 )
-def test_disable_host_mount(tmp_path: Path, container_engine, config, should_have_host_mount):
+def test_disable_host_mount(
+    tmp_path: Path,
+    container_engine: OCIContainerEngineConfig,
+    config: str,
+    should_have_host_mount: bool,
+) -> None:
     if detect_ci_provider() in {CIProvider.circle_ci, CIProvider.gitlab}:
         pytest.skip("Skipping test because docker on this platform does not support host mounts")
     if sys.platform.startswith("darwin"):
@@ -536,7 +543,9 @@ def test_disable_host_mount(tmp_path: Path, container_engine, config, should_hav
 
 
 @pytest.mark.parametrize("platform", list(OCIPlatform))
-def test_local_image(container_engine, platform, tmp_path: Path):
+def test_local_image(
+    container_engine: OCIContainerEngineConfig, platform: OCIPlatform, tmp_path: Path
+) -> None:
     if (
         detect_ci_provider() in {CIProvider.travis_ci}
         and pm in {"s390x", "ppc64le"}
diff --git a/unit_test/options_test.py b/unit_test/options_test.py
index c19c6619f..061396552 100644
--- a/unit_test/options_test.py
+++ b/unit_test/options_test.py
@@ -178,7 +178,7 @@ def test_toml_environment_evil(tmp_path, env_var_value):
         (r'TEST_VAR="before\\$after"', "before$after"),
     ],
 )
-def test_toml_environment_quoting(tmp_path: Path, toml_assignment, result_value):
+def test_toml_environment_quoting(tmp_path: Path, toml_assignment: str, result_value: str) -> None:
     args = CommandLineArguments.defaults()
     args.package_dir = tmp_path
 
@@ -255,8 +255,12 @@ def test_toml_environment_quoting(tmp_path: Path, toml_assignment, result_value)
     ],
 )
 def test_container_engine_option(
-    tmp_path: Path, toml_assignment, result_name, result_create_args, result_disable_host_mount
-):
+    tmp_path: Path,
+    toml_assignment: str,
+    result_name: str,
+    result_create_args: tuple[str, ...],
+    result_disable_host_mount: bool,
+) -> None:
     args = CommandLineArguments.defaults()
     args.package_dir = tmp_path
 
@@ -326,7 +330,9 @@ def test_environment_pass_references():
         ),
     ],
 )
-def test_build_frontend_option(tmp_path: Path, toml_assignment, result_name, result_args):
+def test_build_frontend_option(
+    tmp_path: Path, toml_assignment: str, result_name: str, result_args: list[str]
+) -> None:
     args = CommandLineArguments.defaults()
     args.package_dir = tmp_path
 
@@ -350,7 +356,7 @@ def test_build_frontend_option(tmp_path: Path, toml_assignment, result_name, res
         assert parsed_build_frontend is None
 
 
-def test_override_inherit_environment(tmp_path: Path):
+def test_override_inherit_environment(tmp_path: Path) -> None:
     args = CommandLineArguments.defaults()
     args.package_dir = tmp_path
 
@@ -385,7 +391,7 @@ def test_override_inherit_environment(tmp_path: Path):
     }
 
 
-def test_override_inherit_environment_with_references(tmp_path: Path):
+def test_override_inherit_environment_with_references(tmp_path: Path) -> None:
     args = CommandLineArguments.defaults()
     args.package_dir = tmp_path
 
@@ -434,7 +440,7 @@ def test_override_inherit_environment_with_references(tmp_path: Path):
 )
 def test_free_threaded_support(
     tmp_path: Path, toml_assignment: str, env: dict[str, str], expected_result: bool
-):
+) -> None:
     args = CommandLineArguments.defaults()
     args.package_dir = tmp_path
 
diff --git a/unit_test/utils_test.py b/unit_test/utils_test.py
index b433800a5..e3b87be86 100644
--- a/unit_test/utils_test.py
+++ b/unit_test/utils_test.py
@@ -76,7 +76,7 @@ def test_prepare_command():
         ("foo-0.1-py38-none-win_amd64.whl", "pp310-win_amd64"),
     ],
 )
-def test_find_compatible_wheel_found(wheel: str, identifier: str):
+def test_find_compatible_wheel_found(wheel: str, identifier: str) -> None:
     wheel_ = PurePath(wheel)
     found = find_compatible_wheel([wheel_], identifier)
     assert found is wheel_
@@ -96,7 +96,7 @@ def test_find_compatible_wheel_found(wheel: str, identifier: str):
         ("foo-0.1-cp38-cp38-win_amd64.whl", "cp310-win_amd64"),
     ],
 )
-def test_find_compatible_wheel_not_found(wheel: str, identifier: str):
+def test_find_compatible_wheel_not_found(wheel: str, identifier: str) -> None:
     assert find_compatible_wheel([PurePath(wheel)], identifier) is None
 
 
diff --git a/unit_test/validate_schema_test.py b/unit_test/validate_schema_test.py
index 698353990..bb102bb25 100644
--- a/unit_test/validate_schema_test.py
+++ b/unit_test/validate_schema_test.py
@@ -45,7 +45,7 @@ def test_validate_container_engine():
 
 
 @pytest.mark.parametrize("platform", ["macos", "windows"])
-def test_validate_bad_container_engine(platform: str):
+def test_validate_bad_container_engine(platform: str) -> None:
     """
     container-engine is not a valid option for macos or windows
     """