diff --git a/.travis.yml b/.travis.yml
index 855b565c..c30a4ab6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -35,6 +35,8 @@ jobs:
       language: shell
       before_install:
        - choco install python3 --version 3.6.8 --no-progress -y
+       # Update root certificates to fix SSL error; see http://www.chawn.com/RootCerts.htm
+       - powershell "md C:\temp\certs; CertUtil -generateSSTFromWU C:\temp\certs\RootStore.sst; Get-ChildItem -Path C:\\temp\certs\Rootstore.sst | Import-Certificate -CertStoreLocation Cert:\\LocalMachine\\Root\\ | out-null"
       env:
         - PYTHON=C:\\Python36\\python
 
diff --git a/README.md b/README.md
index 6842b249..d3805547 100644
--- a/README.md
+++ b/README.md
@@ -22,11 +22,13 @@ What does it do?
 | CPython 3.6     | ✅ | ✅  | ✅  | ✅ | ✅ | ✅  | ✅  | ✅² |
 | CPython 3.7     | ✅ | ✅  | ✅  | ✅ | ✅ | ✅  | ✅  | ✅² |
 | CPython 3.8     | ✅ | ✅  | ✅  | ✅ | ✅ | ✅  | ✅  | ✅² |
+| CPython 3.9³    | 🛠 | 🛠  | 🛠  | 🛠 | 🛠 | 🛠  | 🛠  |    |
 | PyPy 2.7 v7.3.0 | ✅ |     | ✅  | ✅ |    |     |     |     |
 | PyPy 3.6 v7.3.0 | ✅ |     | ✅  | ✅ |    |     |     |     |
 
 <sup>¹ Not supported on Travis</sup><br>
-<sup>² Beta support until Travis CI fixes <a href="https://travis-ci.community/t/no-space-left-on-device-for-system-z/5954/11">a bug</a></sup>
+<sup>² Beta support until Travis CI fixes <a href="https://travis-ci.community/t/no-space-left-on-device-for-system-z/5954/11">a bug</a></sup><br>
+<sup>³ Python 3.9 is not yet ABI stable, so you shouldn't publish wheels with it yet. But if you want to check that your wheels build on Python 3.9, try our [`python3.9` branch](https://github.com/joerick/cibuildwheel/pull/382)!</sup>
 
 - Builds manylinux, macOS and Windows wheels for CPython and PyPy using Azure Pipelines, Travis CI, AppVeyor, and CircleCI
 - Bundles shared library dependencies on Linux and macOS through [auditwheel](https://github.com/pypa/auditwheel) and [delocate](https://github.com/matthew-brett/delocate)
diff --git a/appveyor.yml b/appveyor.yml
index 4bf0a18f..401eeb11 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -10,6 +10,11 @@ environment:
     - APPVEYOR_BUILD_WORKER_IMAGE: macos-mojave
       APPVEYOR_JOB_NAME: "python37-x64-macos-mojave"
 
+# while pypy libffi dependency is failing the build, allow failures on macos
+matrix:	
+  allow_failures:	
+    - APPVEYOR_BUILD_WORKER_IMAGE: macos-mojave
+
 stack: python 3.7
 
 build: off
diff --git a/bin/run_tests.py b/bin/run_tests.py
index 93c23e88..117f8b9f 100755
--- a/bin/run_tests.py
+++ b/bin/run_tests.py
@@ -3,10 +3,11 @@
 import os
 import subprocess
 import sys
+from pathlib import Path
 
 if __name__ == '__main__':
     # move cwd to the project root
-    os.chdir(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+    os.chdir(Path(__file__).resolve().parents[1])
 
     # run the unit tests
     subprocess.check_call([sys.executable, '-m', 'pytest', 'unit_test'])
diff --git a/cibuildwheel/__main__.py b/cibuildwheel/__main__.py
index 40241ac1..137bc19e 100644
--- a/cibuildwheel/__main__.py
+++ b/cibuildwheel/__main__.py
@@ -4,6 +4,7 @@ import sys
 import textwrap
 import traceback
 from configparser import ConfigParser
+from pathlib import Path
 
 from typing import Any, Dict, List, Optional, overload
 
@@ -20,6 +21,7 @@ from cibuildwheel.util import (
     BuildSelector,
     DependencyConstraints,
     Unbuffered,
+    resources_dir,
 )
 
 
@@ -114,8 +116,8 @@ def main() -> None:
                   file=sys.stderr)
             exit(2)
 
-    package_dir = args.package_dir
-    output_dir = args.output_dir
+    package_dir = Path(args.package_dir)
+    output_dir = Path(args.output_dir)
 
     if platform == 'linux':
         repair_command_default = 'auditwheel repair -w {dest_dir} {wheel}'
@@ -149,7 +151,8 @@ def main() -> None:
     elif dependency_versions == 'latest':
         dependency_constraints = None
     else:
-        dependency_constraints = DependencyConstraints(dependency_versions)
+        dependency_versions_path = Path(dependency_versions)
+        dependency_constraints = DependencyConstraints(dependency_versions_path)
 
     if test_extras:
         test_extras = f'[{test_extras}]'
@@ -163,7 +166,7 @@ def main() -> None:
     # This needs to be passed on to the docker container in linux.py
     os.environ['CIBUILDWHEEL'] = '1'
 
-    if not any(os.path.exists(os.path.join(package_dir, name))
+    if not any((package_dir / name).exists()
                for name in ["setup.py", "setup.cfg", "pyproject.toml"]):
         print('cibuildwheel: Could not find setup.py, setup.cfg or pyproject.toml at root of package', file=sys.stderr)
         exit(2)
@@ -174,9 +177,7 @@ def main() -> None:
 
     manylinux_images: Optional[Dict[str, str]] = None
     if platform == 'linux':
-        pinned_docker_images_file = os.path.join(
-            os.path.dirname(__file__), 'resources', 'pinned_docker_images.cfg'
-        )
+        pinned_docker_images_file = resources_dir / 'pinned_docker_images.cfg'
         all_pinned_docker_images = ConfigParser()
         all_pinned_docker_images.read(pinned_docker_images_file)
         # all_pinned_docker_images looks like a dict of dicts, e.g.
@@ -224,8 +225,8 @@ def main() -> None:
 
     print_preamble(platform, build_options)
 
-    if not os.path.exists(output_dir):
-        os.makedirs(output_dir)
+    if not output_dir.exists():
+        output_dir.mkdir(parents=True)
 
     if platform == 'linux':
         cibuildwheel.linux.build(build_options)
diff --git a/cibuildwheel/linux.py b/cibuildwheel/linux.py
index 3a660ef1..99e779c4 100644
--- a/cibuildwheel/linux.py
+++ b/cibuildwheel/linux.py
@@ -5,6 +5,7 @@ import subprocess
 import sys
 import textwrap
 import uuid
+from pathlib import Path, PurePath
 
 from typing import List, NamedTuple, Optional, Union
 
@@ -104,10 +105,12 @@ def build(options: BuildOptions) -> None:
         ('pp', 'manylinux_x86_64', options.manylinux_images['pypy_x86_64']),
     ]
 
-    if not os.path.realpath(options.package_dir).startswith(os.path.realpath('.')):
+    cwd = Path.cwd()
+    abs_package_dir = options.package_dir.resolve()
+    if cwd != abs_package_dir and cwd not in abs_package_dir.parents:
         raise Exception('package_dir must be inside the working directory')
 
-    container_package_dir = os.path.join('/project', os.path.relpath(options.package_dir, '.'))
+    container_package_dir = PurePath('/project') / abs_package_dir.relative_to(cwd)
 
     for implementation, platform_tag, docker_image in platforms:
         platform_configs = [c for c in python_configurations if c.identifier.startswith(implementation) and c.identifier.endswith(platform_tag)]
@@ -200,7 +203,6 @@ def build(options: BuildOptions) -> None:
                             pip install {dependency_install_flags} virtualenv
                             venv_dir=`mktemp -d`/venv
                             python -m virtualenv --no-download "$venv_dir"
-                            export __CIBW_VIRTUALENV_PATH__=$venv_dir
 
                             # run the tests in a subshell to keep that `activate`
                             # script from polluting the env
@@ -273,7 +275,7 @@ def build(options: BuildOptions) -> None:
             # copy the output back into the host
             call(['docker', 'cp',
                   container_name + ':/output/.',
-                  os.path.abspath(options.output_dir)])
+                  str(options.output_dir.resolve())])
         except subprocess.CalledProcessError as error:
             troubleshoot(options.package_dir, error)
             exit(1)
@@ -282,16 +284,11 @@ def build(options: BuildOptions) -> None:
             call(['docker', 'rm', '--force', '-v', container_name])
 
 
-def troubleshoot(package_dir: str, error: Exception) -> None:
+def troubleshoot(package_dir: Path, error: Exception) -> None:
     if (isinstance(error, subprocess.CalledProcessError) and 'exec' in error.cmd):
         # the bash script failed
         print('Checking for common errors...')
-        so_files = []
-        for root, dirs, files in os.walk(package_dir):
-            for name in files:
-                _, ext = os.path.splitext(name)
-                if ext == '.so':
-                    so_files.append(os.path.join(root, name))
+        so_files = list(package_dir.glob('**/*.so'))
 
         if so_files:
             print(textwrap.dedent('''
@@ -305,5 +302,5 @@ def troubleshoot(package_dir: str, error: Exception) -> None:
             '''))
 
             print('  Files detected:')
-            print('\n'.join(['    ' + f for f in so_files]))
+            print('\n'.join([f'    {f}' for f in so_files]))
             print('')
diff --git a/cibuildwheel/macos.py b/cibuildwheel/macos.py
index 745c1557..2fd28d20 100644
--- a/cibuildwheel/macos.py
+++ b/cibuildwheel/macos.py
@@ -4,7 +4,7 @@ import shutil
 import subprocess
 import sys
 import tempfile
-from glob import glob
+from pathlib import Path
 
 from typing import Dict, List, Optional, NamedTuple, Union
 
@@ -52,41 +52,41 @@ def get_python_configurations(build_selector: BuildSelector) -> List[PythonConfi
     return [c for c in python_configurations if build_selector(c.identifier)]
 
 
-SYMLINKS_DIR = '/tmp/cibw_bin'
+SYMLINKS_DIR = Path('/tmp/cibw_bin')
 
 
-def make_symlinks(installation_bin_path: str, python_executable: str, pip_executable: str) -> None:
-    assert os.path.exists(os.path.join(installation_bin_path, python_executable))
+def make_symlinks(installation_bin_path: Path, python_executable: str, pip_executable: str) -> None:
+    assert (installation_bin_path / python_executable).exists()
 
     # Python bin folders on Mac don't symlink `python3` to `python`, and neither
     # does PyPy for `pypy` or `pypy3`, so we do that so `python` and `pip` always
     # point to the active configuration.
-    if os.path.exists(SYMLINKS_DIR):
+    if SYMLINKS_DIR.exists():
         shutil.rmtree(SYMLINKS_DIR)
-    os.makedirs(SYMLINKS_DIR)
+    SYMLINKS_DIR.mkdir(parents=True)
 
-    os.symlink(os.path.join(installation_bin_path, python_executable), os.path.join(SYMLINKS_DIR, 'python'))
-    os.symlink(os.path.join(installation_bin_path, python_executable + '-config'), os.path.join(SYMLINKS_DIR, 'python-config'))
-    os.symlink(os.path.join(installation_bin_path, pip_executable), os.path.join(SYMLINKS_DIR, 'pip'))
+    (SYMLINKS_DIR / 'python').symlink_to(installation_bin_path / python_executable)
+    (SYMLINKS_DIR / 'python-config').symlink_to(installation_bin_path / (python_executable + '-config'))
+    (SYMLINKS_DIR / 'pip').symlink_to(installation_bin_path / pip_executable)
 
 
-def install_cpython(version: str, url: str) -> str:
+def install_cpython(version: str, url: str) -> Path:
     installed_system_packages = subprocess.check_output(['pkgutil', '--pkgs'], universal_newlines=True).splitlines()
 
     # if this version of python isn't installed, get it from python.org and install
     python_package_identifier = f'org.python.Python.PythonFramework-{version}'
     if python_package_identifier not in installed_system_packages:
         # download the pkg
-        download(url, '/tmp/Python.pkg')
+        download(url, Path('/tmp/Python.pkg'))
         # install
         call(['sudo', 'installer', '-pkg', '/tmp/Python.pkg', '-target', '/'])
         # patch open ssl
         if version == '3.5':
             open_ssl_patch_url = f'https://github.com/mayeut/patch-macos-python-openssl/releases/download/v1.0.2u/patch-macos-python-{version}-openssl-v1.0.2u.tar.gz'
-            download(open_ssl_patch_url, '/tmp/python-patch.tar.gz')
+            download(open_ssl_patch_url, Path('/tmp/python-patch.tar.gz'))
             call(['sudo', 'tar', '-C', f'/Library/Frameworks/Python.framework/Versions/{version}/', '-xmf', '/tmp/python-patch.tar.gz'])
 
-    installation_bin_path = f'/Library/Frameworks/Python.framework/Versions/{version}/bin'
+    installation_bin_path = Path(f'/Library/Frameworks/Python.framework/Versions/{version}/bin')
     python_executable = 'python3' if version[0] == '3' else 'python'
     pip_executable = 'pip3' if version[0] == '3' else 'pip'
     make_symlinks(installation_bin_path, python_executable, pip_executable)
@@ -94,16 +94,18 @@ def install_cpython(version: str, url: str) -> str:
     return installation_bin_path
 
 
-def install_pypy(version: str, url: str) -> str:
+def install_pypy(version: str, url: str) -> Path:
     pypy_tar_bz2 = url.rsplit('/', 1)[-1]
-    assert pypy_tar_bz2.endswith(".tar.bz2")
-    pypy_base_filename = os.path.splitext(os.path.splitext(pypy_tar_bz2)[0])[0]
-    installation_path = os.path.join('/tmp', pypy_base_filename)
-    if not os.path.exists(installation_path):
-        download(url, os.path.join("/tmp", pypy_tar_bz2))
-        call(['tar', '-C', '/tmp', '-xf', os.path.join("/tmp", pypy_tar_bz2)])
+    extension = ".tar.bz2"
+    assert pypy_tar_bz2.endswith(extension)
+    pypy_base_filename = pypy_tar_bz2[:-len(extension)]
+    installation_path = Path('/tmp') / pypy_base_filename
+    if not installation_path.exists():
+        downloaded_tar_bz2 = Path("/tmp") / pypy_tar_bz2
+        download(url, downloaded_tar_bz2)
+        call(['tar', '-C', '/tmp', '-xf', str(downloaded_tar_bz2)])
 
-    installation_bin_path = os.path.join(installation_path, 'bin')
+    installation_bin_path = installation_path / 'bin'
     python_executable = 'pypy3' if version[0] == '3' else 'pypy'
     pip_executable = 'pip3' if version[0] == '3' else 'pip'
     make_symlinks(installation_bin_path, python_executable, pip_executable)
@@ -121,8 +123,8 @@ def setup_python(python_configuration: PythonConfiguration, dependency_constrain
 
     env = os.environ.copy()
     env['PATH'] = os.pathsep.join([
-        SYMLINKS_DIR,
-        installation_bin_path,
+        str(SYMLINKS_DIR),
+        str(installation_bin_path),
         env['PATH'],
     ])
 
@@ -144,8 +146,8 @@ def setup_python(python_configuration: PythonConfiguration, dependency_constrain
         exit(1)
 
     # install pip & wheel
-    call(['python', get_pip_script] + dependency_constraint_flags, env=env, cwd="/tmp")
-    assert os.path.exists(os.path.join(installation_bin_path, 'pip'))
+    call(['python', str(get_pip_script)] + dependency_constraint_flags, env=env, cwd="/tmp")
+    assert (installation_bin_path / 'pip').exists()
     call(['which', 'pip'], env=env)
     call(['pip', '--version'], env=env)
     which_pip = subprocess.check_output(['which', 'pip'], env=env, universal_newlines=True).strip()
@@ -170,9 +172,9 @@ def setup_python(python_configuration: PythonConfiguration, dependency_constrain
 
 
 def build(options: BuildOptions) -> None:
-    temp_dir = tempfile.mkdtemp(prefix='cibuildwheel')
-    built_wheel_dir = os.path.join(temp_dir, 'built_wheel')
-    repaired_wheel_dir = os.path.join(temp_dir, 'repaired_wheel')
+    temp_dir = Path(tempfile.mkdtemp(prefix='cibuildwheel'))
+    built_wheel_dir = temp_dir / 'built_wheel'
+    repaired_wheel_dir = temp_dir / 'repaired_wheel'
 
     python_configurations = get_python_configurations(options.build_selector)
 
@@ -180,7 +182,7 @@ def build(options: BuildOptions) -> None:
         dependency_constraint_flags = []
         if options.dependency_constraints:
             dependency_constraint_flags = [
-                '-c', options.dependency_constraints.get_for_python_version(config.version)
+                '-c', str(options.dependency_constraints.get_for_python_version(config.version))
             ]
 
         env = setup_python(config, dependency_constraint_flags, options.environment)
@@ -191,40 +193,41 @@ def build(options: BuildOptions) -> None:
             call(before_build_prepared, env=env, shell=True)
 
         # build the wheel
-        if os.path.exists(built_wheel_dir):
+        if built_wheel_dir.exists():
             shutil.rmtree(built_wheel_dir)
-        os.makedirs(built_wheel_dir)
-        call(['pip', 'wheel', options.package_dir, '-w', built_wheel_dir, '--no-deps'] + get_build_verbosity_extra_flags(options.build_verbosity), env=env)
-        built_wheel = glob(os.path.join(built_wheel_dir, '*.whl'))[0]
+        built_wheel_dir.mkdir(parents=True)
+        # Path.resolve() is needed. Without it pip wheel may try to fetch package from pypi.org
+        # see https://github.com/joerick/cibuildwheel/pull/369
+        call(['pip', 'wheel', str(options.package_dir.resolve()), '-w', str(built_wheel_dir), '--no-deps'] + get_build_verbosity_extra_flags(options.build_verbosity), env=env)
+        built_wheel = next(built_wheel_dir.glob('*.whl'))
 
         # repair the wheel
-        if os.path.exists(repaired_wheel_dir):
+        if repaired_wheel_dir.exists():
             shutil.rmtree(repaired_wheel_dir)
-        os.makedirs(repaired_wheel_dir)
-        if built_wheel.endswith('none-any.whl') or not options.repair_command:
+        repaired_wheel_dir.mkdir(parents=True)
+        if built_wheel.name.endswith('none-any.whl') or not options.repair_command:
             # pure Python wheel or empty repair command
-            shutil.move(built_wheel, repaired_wheel_dir)
+            built_wheel.rename(repaired_wheel_dir / built_wheel.name)
         else:
             repair_command_prepared = prepare_command(options.repair_command, wheel=built_wheel, dest_dir=repaired_wheel_dir)
             call(repair_command_prepared, env=env, shell=True)
-        repaired_wheel = glob(os.path.join(repaired_wheel_dir, '*.whl'))[0]
+        repaired_wheel = next(repaired_wheel_dir.glob('*.whl'))
 
         if options.test_command:
             # set up a virtual environment to install and test from, to make sure
             # there are no dependencies that were pulled in at build time.
             call(['pip', 'install', 'virtualenv'] + dependency_constraint_flags, env=env)
-            venv_dir = tempfile.mkdtemp()
+            venv_dir = Path(tempfile.mkdtemp())
 
             # Use --no-download to ensure determinism by using seed libraries
             # built into virtualenv
-            call(['python', '-m', 'virtualenv', '--no-download', venv_dir], env=env)
+            call(['python', '-m', 'virtualenv', '--no-download', str(venv_dir)], env=env)
 
             virtualenv_env = env.copy()
             virtualenv_env['PATH'] = os.pathsep.join([
-                os.path.join(venv_dir, 'bin'),
+                str(venv_dir / 'bin'),
                 virtualenv_env['PATH'],
             ])
-            virtualenv_env["__CIBW_VIRTUALENV_PATH__"] = venv_dir
 
             # check that we are using the Python from the virtual environment
             call(['which', 'python'], env=virtualenv_env)
@@ -234,7 +237,7 @@ def build(options: BuildOptions) -> None:
                 call(before_test_prepared, env=virtualenv_env, shell=True)
 
             # install the wheel
-            call(['pip', 'install', repaired_wheel + options.test_extras], env=virtualenv_env)
+            call(['pip', 'install', str(repaired_wheel) + options.test_extras], env=virtualenv_env)
 
             # test the wheel
             if options.test_requires:
@@ -245,8 +248,8 @@ def build(options: BuildOptions) -> None:
             # and not the repo code)
             test_command_prepared = prepare_command(
                 options.test_command,
-                project=os.path.abspath('.'),
-                package=os.path.abspath(options.package_dir)
+                project=Path('.').resolve(),
+                package=options.package_dir.resolve()
             )
             call(test_command_prepared, cwd=os.environ['HOME'], env=virtualenv_env, shell=True)
 
@@ -254,5 +257,4 @@ def build(options: BuildOptions) -> None:
             shutil.rmtree(venv_dir)
 
         # we're all done here; move it to output (overwrite existing)
-        dst = os.path.join(options.output_dir, os.path.basename(repaired_wheel))
-        shutil.move(repaired_wheel, dst)
+        repaired_wheel.replace(options.output_dir / repaired_wheel.name)
diff --git a/cibuildwheel/util.py b/cibuildwheel/util.py
index 499954b9..feef6185 100644
--- a/cibuildwheel/util.py
+++ b/cibuildwheel/util.py
@@ -1,14 +1,15 @@
 import os
 import urllib.request
 from fnmatch import fnmatch
+from pathlib import Path
 from time import sleep
 
-from typing import Dict, List, NamedTuple, Optional
+from typing import Dict, List, NamedTuple, Optional, Union
 
 from .environment import ParsedEnvironment
 
 
-def prepare_command(command: str, **kwargs: str) -> str:
+def prepare_command(command: str, **kwargs: Union[str, os.PathLike]) -> str:
     '''
     Preprocesses a command by expanding variables like {python}.
 
@@ -58,11 +59,11 @@ class Unbuffered:
         return getattr(self.stream, attr)
 
 
-def download(url: str, dest: str) -> None:
-    print('+ Download ' + url + ' to ' + dest)
-    dest_dir = os.path.dirname(dest)
-    if not os.path.exists(dest_dir):
-        os.makedirs(dest_dir)
+def download(url: str, dest: Path) -> None:
+    print(f'+ Download {url} to {dest}')
+    dest_dir = dest.parent
+    if not dest_dir.exists():
+        dest_dir.mkdir(parents=True)
 
     repeat_num = 3
     for i in range(repeat_num):
@@ -76,40 +77,39 @@ def download(url: str, dest: str) -> None:
         break
 
     try:
-        with open(dest, 'wb') as file:
-            file.write(response.read())
+        dest.write_bytes(response.read())
     finally:
         response.close()
 
 
 class DependencyConstraints:
-    def __init__(self, base_file_path: str):
-        assert os.path.exists(base_file_path)
-        self.base_file_path = os.path.abspath(base_file_path)
+    def __init__(self, base_file_path: Path):
+        assert base_file_path.exists()
+        self.base_file_path = base_file_path.resolve()
 
     @staticmethod
     def with_defaults() -> 'DependencyConstraints':
         return DependencyConstraints(
-            base_file_path=os.path.join(os.path.dirname(__file__), 'resources', 'constraints.txt')
+            base_file_path=resources_dir / 'constraints.txt'
         )
 
-    def get_for_python_version(self, version: str) -> str:
+    def get_for_python_version(self, version: str) -> Path:
         version_parts = version.split('.')
 
         # try to find a version-specific dependency file e.g. if
         # ./constraints.txt is the base, look for ./constraints-python27.txt
-        base, ext = os.path.splitext(self.base_file_path)
-        specific = base + f'-python{version_parts[0]}{version_parts[1]}'
-        specific_file_path = specific + ext
-        if os.path.exists(specific_file_path):
+        specific_stem = self.base_file_path.stem + f'-python{version_parts[0]}{version_parts[1]}'
+        specific_name = specific_stem + self.base_file_path.suffix
+        specific_file_path = self.base_file_path.with_name(specific_name)
+        if specific_file_path.exists():
             return specific_file_path
         else:
             return self.base_file_path
 
 
 class BuildOptions(NamedTuple):
-    package_dir: str
-    output_dir: str
+    package_dir: Path
+    output_dir: Path
     build_selector: BuildSelector
     environment: ParsedEnvironment
     before_build: Optional[str]
@@ -123,5 +123,5 @@ class BuildOptions(NamedTuple):
     build_verbosity: int
 
 
-resources_dir = os.path.abspath(os.path.join(os.path.dirname(__file__), 'resources'))
-get_pip_script = os.path.join(resources_dir, 'get-pip.py')
+resources_dir = Path(__file__).resolve().parent / 'resources'
+get_pip_script = resources_dir / 'get-pip.py'
diff --git a/cibuildwheel/windows.py b/cibuildwheel/windows.py
index 6a62b63d..63b22b48 100644
--- a/cibuildwheel/windows.py
+++ b/cibuildwheel/windows.py
@@ -3,7 +3,7 @@ import shutil
 import subprocess
 import sys
 import tempfile
-from glob import glob
+from pathlib import Path
 from zipfile import ZipFile
 import toml
 
@@ -20,7 +20,7 @@ from .util import (
 )
 
 
-IS_RUNNING_ON_AZURE = os.path.exists('C:\\hostedtoolcache')
+IS_RUNNING_ON_AZURE = Path('C:\\hostedtoolcache').exists()
 IS_RUNNING_ON_TRAVIS = os.environ.get('TRAVIS_OS_NAME') == 'windows'
 
 
@@ -72,36 +72,38 @@ def get_python_configurations(build_selector: BuildSelector) -> List[PythonConfi
     return python_configurations
 
 
-def extract_zip(zip_src: str, dest: str) -> None:
+def extract_zip(zip_src: Path, dest: Path) -> None:
     with ZipFile(zip_src) as zip:
         zip.extractall(dest)
 
 
-def install_cpython(version: str, arch: str, nuget: str) -> str:
+def install_cpython(version: str, arch: str, nuget: Path) -> Path:
     nuget_args = get_nuget_args(version, arch)
-    installation_path = os.path.join(nuget_args[-1], nuget_args[0] + '.' + version, 'tools')
-    shell([nuget, 'install'] + nuget_args)
+    installation_path = Path(nuget_args[-1]) / (nuget_args[0] + '.' + version) / 'tools'
+    shell([str(nuget), 'install'] + nuget_args)
     return installation_path
 
 
-def install_pypy(version: str, arch: str, url: str) -> str:
+def install_pypy(version: str, arch: str, url: str) -> Path:
     assert arch == '32'
     # Inside the PyPy zip file is a directory with the same name
     zip_filename = url.rsplit('/', 1)[-1]
-    installation_path = os.path.join('C:\\cibw', os.path.splitext(zip_filename)[0])
-    if not os.path.exists(installation_path):
-        pypy_zip = os.path.join('C:\\cibw', zip_filename)
+    extension = ".zip"
+    assert zip_filename.endswith(extension)
+    installation_path = Path('C:\\cibw') / zip_filename[:-len(extension)]
+    if not installation_path.exists():
+        pypy_zip = Path('C:\\cibw') / zip_filename
         download(url, pypy_zip)
         # Extract to the parent directory because the zip file still contains a directory
-        extract_zip(pypy_zip, os.path.dirname(installation_path))
+        extract_zip(pypy_zip, installation_path.parent)
         pypy_exe = 'pypy3.exe' if version[0] == '3' else 'pypy.exe'
-        shell(['mklink', os.path.join(installation_path, 'python.exe'), os.path.join(installation_path, pypy_exe)])
+        (installation_path / 'python.exe').symlink_to(installation_path / pypy_exe)
     return installation_path
 
 
 def setup_python(python_configuration: PythonConfiguration, dependency_constraint_flags: List[str], environment: ParsedEnvironment) -> Dict[str, str]:
-    nuget = 'C:\\cibw\\nuget.exe'
-    if not os.path.exists(nuget):
+    nuget = Path('C:\\cibw\\nuget.exe')
+    if not nuget.exists():
         download('https://dist.nuget.org/win-x86-commandline/latest/nuget.exe', nuget)
 
     if python_configuration.identifier.startswith('cp'):
@@ -112,15 +114,15 @@ def setup_python(python_configuration: PythonConfiguration, dependency_constrain
     else:
         raise ValueError("Unknown Python implementation")
 
-    assert os.path.exists(os.path.join(installation_path, 'python.exe'))
+    assert (installation_path / 'python.exe').exists()
 
     # set up PATH and environment variables for run_with_env
     env = os.environ.copy()
     env['PYTHON_VERSION'] = python_configuration.version
     env['PYTHON_ARCH'] = python_configuration.arch
     env['PATH'] = os.pathsep.join([
-        installation_path,
-        os.path.join(installation_path, 'Scripts'),
+        str(installation_path),
+        str(installation_path / 'Scripts'),
         env['PATH']
     ])
     # update env with results from CIBW_ENVIRONMENT
@@ -131,16 +133,16 @@ def setup_python(python_configuration: PythonConfiguration, dependency_constrain
     shell(['python', '--version'], env=env)
     shell(['python', '-c', '"import struct; print(struct.calcsize(\'P\') * 8)"'], env=env)
     where_python = subprocess.check_output(['where', 'python'], env=env, universal_newlines=True).splitlines()[0].strip()
-    if where_python != os.path.join(installation_path, 'python.exe'):
+    if where_python != str(installation_path / 'python.exe'):
         print("cibuildwheel: python available on PATH doesn't match our installed instance. If you have modified PATH, ensure that you don't overwrite cibuildwheel's entry or insert python above it.", file=sys.stderr)
         exit(1)
 
     # make sure pip is installed
-    if not os.path.exists(os.path.join(installation_path, 'Scripts', 'pip.exe')):
-        shell(['python', get_pip_script] + dependency_constraint_flags, env=env, cwd="C:\\cibw")
-    assert os.path.exists(os.path.join(installation_path, 'Scripts', 'pip.exe'))
+    if not (installation_path / 'Scripts' / 'pip.exe').exists():
+        shell(['python', str(get_pip_script)] + dependency_constraint_flags, env=env, cwd="C:\\cibw")
+    assert (installation_path / 'Scripts' / 'pip.exe').exists()
     where_pip = subprocess.check_output(['where', 'pip'], env=env, universal_newlines=True).splitlines()[0].strip()
-    if where_pip.strip() != os.path.join(installation_path, 'Scripts', 'pip.exe'):
+    if where_pip.strip() != str(installation_path / 'Scripts' / 'pip.exe'):
         print("cibuildwheel: pip available on PATH doesn't match our installed instance. If you have modified PATH, ensure that you don't overwrite cibuildwheel's entry or insert pip above it.", file=sys.stderr)
         exit(1)
 
@@ -178,12 +180,12 @@ def pep_518_cp35_workaround(package_dir: str, env: Dict[str, str]) -> None:
 
 
 def build(options: BuildOptions) -> None:
-    temp_dir = tempfile.mkdtemp(prefix='cibuildwheel')
-    built_wheel_dir = os.path.join(temp_dir, 'built_wheel')
-    repaired_wheel_dir = os.path.join(temp_dir, 'repaired_wheel')
+    temp_dir = Path(tempfile.mkdtemp(prefix='cibuildwheel'))
+    built_wheel_dir = temp_dir / 'built_wheel'
+    repaired_wheel_dir = temp_dir / 'repaired_wheel'
 
     # install nuget as best way to provide python
-    nuget = 'C:\\cibw\\nuget.exe'
+    nuget = Path('C:\\cibw\\nuget.exe')
     download('https://dist.nuget.org/win-x86-commandline/latest/nuget.exe', nuget)
 
     python_configurations = get_python_configurations(options.build_selector)
@@ -191,7 +193,7 @@ def build(options: BuildOptions) -> None:
         dependency_constraint_flags = []
         if options.dependency_constraints:
             dependency_constraint_flags = [
-                '-c', options.dependency_constraints.get_for_python_version(config.version)
+                '-c', str(options.dependency_constraints.get_for_python_version(config.version))
             ]
 
         # install Python
@@ -208,42 +210,41 @@ def build(options: BuildOptions) -> None:
             pep_518_cp35_workaround(options.package_dir, env)
 
         # build the wheel
-        if os.path.exists(built_wheel_dir):
+        if built_wheel_dir.exists():
             shutil.rmtree(built_wheel_dir)
-        os.makedirs(built_wheel_dir)
-        shell(['pip', 'wheel', options.package_dir, '-w', built_wheel_dir, '--no-deps'] + get_build_verbosity_extra_flags(options.build_verbosity), env=env)
-        built_wheel = glob(os.path.join(built_wheel_dir, '*.whl'))[0]
+        built_wheel_dir.mkdir(parents=True)
+        # Path.resolve() is needed. Without it pip wheel may try to fetch package from pypi.org
+        # see https://github.com/joerick/cibuildwheel/pull/369
+        shell(['pip', 'wheel', str(options.package_dir.resolve()), '-w', str(built_wheel_dir), '--no-deps'] + get_build_verbosity_extra_flags(options.build_verbosity), env=env)
+        built_wheel = next(built_wheel_dir.glob('*.whl'))
 
         # repair the wheel
-        if os.path.exists(repaired_wheel_dir):
+        if repaired_wheel_dir.exists():
             shutil.rmtree(repaired_wheel_dir)
-        os.makedirs(repaired_wheel_dir)
-        if built_wheel.endswith('none-any.whl') or not options.repair_command:
+        repaired_wheel_dir.mkdir(parents=True)
+        if built_wheel.name.endswith('none-any.whl') or not options.repair_command:
             # pure Python wheel or empty repair command
-            shutil.move(built_wheel, repaired_wheel_dir)
+            built_wheel.rename(repaired_wheel_dir / built_wheel.name)
         else:
             repair_command_prepared = prepare_command(options.repair_command, wheel=built_wheel, dest_dir=repaired_wheel_dir)
             shell([repair_command_prepared], env=env)
-        repaired_wheel = glob(os.path.join(repaired_wheel_dir, '*.whl'))[0]
+        repaired_wheel = next(repaired_wheel_dir.glob('*.whl'))
 
         if options.test_command:
             # set up a virtual environment to install and test from, to make sure
             # there are no dependencies that were pulled in at build time.
             shell(['pip', 'install', 'virtualenv'] + dependency_constraint_flags, env=env)
-            venv_dir = tempfile.mkdtemp()
+            venv_dir = Path(tempfile.mkdtemp())
 
             # Use --no-download to ensure determinism by using seed libraries
             # built into virtualenv
-            shell(['python', '-m', 'virtualenv', '--no-download', venv_dir], env=env)
+            shell(['python', '-m', 'virtualenv', '--no-download', str(venv_dir)], env=env)
 
             virtualenv_env = env.copy()
-
-            venv_script_path = os.path.join(venv_dir, 'Scripts')
             virtualenv_env['PATH'] = os.pathsep.join([
-                venv_script_path,
+                str(venv_dir / 'Scripts'),
                 virtualenv_env['PATH'],
             ])
-            virtualenv_env["__CIBW_VIRTUALENV_PATH__"] = venv_dir
 
             # check that we are using the Python from the virtual environment
             shell(['which', 'python'], env=virtualenv_env)
@@ -257,7 +258,7 @@ def build(options: BuildOptions) -> None:
                 shell([before_test_prepared], env=virtualenv_env)
 
             # install the wheel
-            shell(['pip', 'install', repaired_wheel + options.test_extras], env=virtualenv_env)
+            shell(['pip', 'install', str(repaired_wheel) + options.test_extras], env=virtualenv_env)
 
             # test the wheel
             if options.test_requires:
@@ -268,8 +269,8 @@ def build(options: BuildOptions) -> None:
             # and not the repo code)
             test_command_prepared = prepare_command(
                 options.test_command,
-                project=os.path.abspath('.'),
-                package=os.path.abspath(options.package_dir)
+                project=Path('.').resolve(),
+                package=options.package_dir.resolve()
             )
             shell([test_command_prepared], cwd='c:\\', env=virtualenv_env)
 
@@ -277,7 +278,4 @@ def build(options: BuildOptions) -> None:
             shutil.rmtree(venv_dir)
 
         # we're all done here; move it to output (remove if already exists)
-        dst = os.path.join(options.output_dir, os.path.basename(repaired_wheel))
-        if os.path.isfile(dst):
-            os.remove(dst)
-        shutil.move(repaired_wheel, dst)
+        repaired_wheel.replace(options.output_dir / repaired_wheel.name)
diff --git a/docs/mkdocs_include_markdown_plugin/mkdocs_include_markdown_plugin/plugin.py b/docs/mkdocs_include_markdown_plugin/mkdocs_include_markdown_plugin/plugin.py
index b6b7a723..f12ea469 100644
--- a/docs/mkdocs_include_markdown_plugin/mkdocs_include_markdown_plugin/plugin.py
+++ b/docs/mkdocs_include_markdown_plugin/mkdocs_include_markdown_plugin/plugin.py
@@ -1,7 +1,6 @@
 import cgi
-import io
-import os
 import re
+from pathlib import Path
 
 import mkdocs
 
@@ -41,13 +40,12 @@ class ImportMarkdownPlugin(mkdocs.plugins.BasePlugin):
         def found_include_tag(match):
             filename = match.group('filename')
 
-            file_path_abs = os.path.join(os.path.dirname(page_src_path), filename)
+            file_path_abs = Path(page_src_path).parent / filename
 
-            if not os.path.exists(file_path_abs):
+            if not file_path_abs.exists():
                 raise ValueError('file not found', filename)
 
-            with io.open(file_path_abs, encoding='utf8') as f:
-                text_to_include = f.read()
+            text_to_include = file_path_abs.read_text(encoding='utf8')
 
             # Allow good practice of having a final newline in the file
             if text_to_include.endswith('\n'):
@@ -60,13 +58,12 @@ class ImportMarkdownPlugin(mkdocs.plugins.BasePlugin):
             start = match.group('start')
             end = match.group('end')
 
-            file_path_abs = os.path.join(os.path.dirname(page_src_path), filename)
+            file_path_abs = Path(page_src_path).parent / filename
 
-            if not os.path.exists(file_path_abs):
+            if not file_path_abs.exists():
                 raise ValueError('file not found', filename)
 
-            with io.open(file_path_abs, encoding='utf8') as f:
-                text_to_include = f.read()
+            text_to_include = file_path_abs.read_text(encoding='utf8')
 
             if start:
                 _, _, text_to_include = text_to_include.partition(start)
diff --git a/setup.py b/setup.py
index 68dbff3a..542d29f7 100644
--- a/setup.py
+++ b/setup.py
@@ -1,15 +1,13 @@
 # -*- coding: utf-8 -*-
-import io
-import os
+from pathlib import Path
 
 try:
     from setuptools import setup
 except ImportError:
     from distutils.core import setup
 
-this_directory = os.path.dirname(__file__)
-with io.open(os.path.join(this_directory, 'README.md'), encoding='utf-8') as f:
-    long_description = f.read()
+this_directory = Path(__file__).parent
+long_description = (this_directory / 'README.md').read_text(encoding='utf-8')
 
 setup(
     name='cibuildwheel',
diff --git a/test/test_dependency_versions.py b/test/test_dependency_versions.py
index 611350f1..2f79bd2a 100644
--- a/test/test_dependency_versions.py
+++ b/test/test_dependency_versions.py
@@ -1,4 +1,3 @@
-import os
 import re
 import pytest
 import textwrap
@@ -39,11 +38,9 @@ VERSION_REGEX = r'([\w-]+)==([^\s]+)'
 
 
 def get_versions_from_constraint_file(constraint_file):
-    with open(constraint_file, encoding='utf8') as f:
-        constraint_file_text = f.read()
+    constraint_file_text = constraint_file.read_text(encoding='utf8')
 
     versions = {}
-
     for package, version in re.findall(VERSION_REGEX, constraint_file_text):
         versions[package] = version
 
@@ -73,7 +70,7 @@ def test_pinned_versions(tmp_path, python_version):
         constraint_filename = 'constraints.txt'
         build_pattern = '[cp]p38-*'
 
-    constraint_file = os.path.join(cibuildwheel.util.resources_dir, constraint_filename)
+    constraint_file = cibuildwheel.util.resources_dir / constraint_filename
     constraint_versions = get_versions_from_constraint_file(constraint_file)
 
     for package in ['pip', 'setuptools', 'wheel', 'virtualenv']:
diff --git a/test/test_projects/base.py b/test/test_projects/base.py
index 5cac80ad..a5710fdf 100644
--- a/test/test_projects/base.py
+++ b/test/test_projects/base.py
@@ -1,5 +1,7 @@
-import os
+from pathlib import Path
+
 import jinja2
+
 from typing import Union, Dict, Any
 
 
@@ -14,6 +16,8 @@ class TestProject:
 
     Write out to the filesystem using `generate`.
     '''
+    __test__ = False  # Have pytest ignore this class on `from .test_projects import TestProject`
+
     files: FilesDict
     template_context: TemplateContext
 
@@ -21,12 +25,12 @@ class TestProject:
         self.files = {}
         self.template_context = {}
 
-    def generate(self, path: str):
+    def generate(self, path: Path):
         for filename, content in self.files.items():
-            file_path = os.path.join(path, filename)
-            os.makedirs(os.path.dirname(file_path), exist_ok=True)
+            file_path = path / filename
+            file_path.parent.mkdir(parents=True, exist_ok=True)
 
-            with open(file_path, 'w', encoding='utf8') as f:
+            with file_path.open('w', encoding='utf8') as f:
                 if isinstance(content, jinja2.Template):
                     content = content.render(self.template_context)
 
diff --git a/test/test_subdir_package.py b/test/test_subdir_package.py
index 53bd9520..14a7a58b 100644
--- a/test/test_subdir_package.py
+++ b/test/test_subdir_package.py
@@ -1,4 +1,4 @@
-import os
+from pathlib import Path
 
 import jinja2
 
@@ -35,7 +35,7 @@ def test(capfd, tmp_path):
     project_dir = tmp_path / 'project'
     subdir_package_project.generate(project_dir)
 
-    package_dir = os.path.join(project_dir, 'src', 'spam')
+    package_dir = Path('src', 'spam')
     # build the wheels
     actual_wheels = utils.cibuildwheel_run(project_dir, package_dir=package_dir, add_env={
         'CIBW_BEFORE_BUILD': 'python {project}/bin/before_build.py',
diff --git a/test/test_testing.py b/test/test_testing.py
index dda833ea..58a38224 100644
--- a/test/test_testing.py
+++ b/test/test_testing.py
@@ -46,12 +46,15 @@ class TestSpam(TestCase):
         self.assertNotEqual(0, spam.system('python -c "exit(1)"'))
 
     def test_virtualenv(self):
-        virtualenv_path = os.environ.get("__CIBW_VIRTUALENV_PATH__")
-        if not virtualenv_path:
-            self.fail("No virtualenv path defined in environment variable __CIBW_VIRTUALENV_PATH__")
+        # sys.prefix is different from sys.base_prefix when running a virtualenv
+        # See https://docs.python.org/3/library/venv.html, which virtualenv seems
+        # to honor in recent releases
+        # Python 2 doesn't have sys.base_prefix by default
+        if not hasattr(sys, 'base_prefix') or sys.prefix == sys.base_prefix:
+            self.fail("Not running in a virtualenv")
 
-        self.assertTrue(path_contains(virtualenv_path, sys.executable))
-        self.assertTrue(path_contains(virtualenv_path, spam.__file__))
+        self.assertTrue(path_contains(sys.prefix, sys.executable))
+        self.assertTrue(path_contains(sys.prefix, spam.__file__))
 
     def test_uname(self):
         if platform.system() == "Windows":
diff --git a/test/utils.py b/test/utils.py
index 15ce402a..217a616f 100644
--- a/test/utils.py
+++ b/test/utils.py
@@ -10,9 +10,10 @@ import shutil
 import subprocess
 import sys
 from contextlib import contextmanager
+from pathlib import Path
 from tempfile import mkdtemp
 
-IS_WINDOWS_RUNNING_ON_AZURE = os.path.exists('C:\\hostedtoolcache')
+IS_WINDOWS_RUNNING_ON_AZURE = Path('C:\\hostedtoolcache').exists()
 IS_WINDOWS_RUNNING_ON_TRAVIS = os.environ.get('TRAVIS_OS_NAME') == 'windows'
 
 
@@ -66,7 +67,7 @@ def cibuildwheel_run(project_path, package_dir='.', env=None, add_env=None, outp
 
     with TemporaryDirectoryIfNone(output_dir) as _output_dir:
         subprocess.check_call(
-            [sys.executable, '-m', 'cibuildwheel', '--output-dir', str(_output_dir), package_dir],
+            [sys.executable, '-m', 'cibuildwheel', '--output-dir', str(_output_dir), str(package_dir)],
             env=env,
             cwd=project_path,
         )
diff --git a/unit_test/dependency_constraints_test.py b/unit_test/dependency_constraints_test.py
index b3fb0cb3..5347011c 100644
--- a/unit_test/dependency_constraints_test.py
+++ b/unit_test/dependency_constraints_test.py
@@ -1,30 +1,16 @@
 from cibuildwheel.util import DependencyConstraints
-import os
+
+from pathlib import Path
 
 
 def test_defaults():
     dependency_constraints = DependencyConstraints.with_defaults()
 
-    project_root = os.path.dirname(os.path.dirname(__file__))
-    resources_dir = os.path.join(project_root, 'cibuildwheel', 'resources')
+    project_root = Path(__file__).parents[1]
+    resources_dir = project_root / 'cibuildwheel' / 'resources'
 
-    assert os.path.samefile(
-        dependency_constraints.base_file_path,
-        os.path.join(resources_dir, 'constraints.txt')
-    )
-    assert os.path.samefile(
-        dependency_constraints.get_for_python_version('3.8'),
-        os.path.join(resources_dir, 'constraints.txt')
-    )
-    assert os.path.samefile(
-        dependency_constraints.get_for_python_version('3.6'),
-        os.path.join(resources_dir, 'constraints-python36.txt')
-    )
-    assert os.path.samefile(
-        dependency_constraints.get_for_python_version('3.5'),
-        os.path.join(resources_dir, 'constraints-python35.txt')
-    )
-    assert os.path.samefile(
-        dependency_constraints.get_for_python_version('2.7'),
-        os.path.join(resources_dir, 'constraints-python27.txt')
-    )
+    assert dependency_constraints.base_file_path.samefile(resources_dir / 'constraints.txt')
+    assert dependency_constraints.get_for_python_version('3.8').samefile(resources_dir / 'constraints.txt')
+    assert dependency_constraints.get_for_python_version('3.6').samefile(resources_dir / 'constraints-python36.txt')
+    assert dependency_constraints.get_for_python_version('3.5').samefile(resources_dir / 'constraints-python35.txt')
+    assert dependency_constraints.get_for_python_version('2.7').samefile(resources_dir / 'constraints-python27.txt')
diff --git a/unit_test/main_tests/conftest.py b/unit_test/main_tests/conftest.py
index cd896915..3f684b6c 100644
--- a/unit_test/main_tests/conftest.py
+++ b/unit_test/main_tests/conftest.py
@@ -1,6 +1,6 @@
-import os
 import subprocess
 import sys
+from pathlib import Path
 
 import pytest
 
@@ -18,7 +18,7 @@ class ArgsInterceptor:
         self.kwargs = kwargs
 
 
-MOCK_PACKAGE_DIR = 'some_package_dir'
+MOCK_PACKAGE_DIR = Path('some_package_dir')
 
 
 @pytest.fixture(autouse=True)
@@ -31,28 +31,33 @@ def mock_protection(monkeypatch):
     def fail_on_call(*args, **kwargs):
         raise RuntimeError("This should never be called")
 
+    def ignore_call(*args, **kwargs):
+        pass
+
     monkeypatch.setattr(subprocess, 'Popen', fail_on_call)
     monkeypatch.setattr(util, 'download', fail_on_call)
     monkeypatch.setattr(windows, 'build', fail_on_call)
     monkeypatch.setattr(linux, 'build', fail_on_call)
     monkeypatch.setattr(macos, 'build', fail_on_call)
 
+    monkeypatch.setattr(Path, 'mkdir', ignore_call)
+
 
 @pytest.fixture(autouse=True)
 def fake_package_dir(monkeypatch):
     '''
     Monkey-patch enough for the main() function to run
     '''
-    real_os_path_exists = os.path.exists
+    real_path_exists = Path.exists
 
-    def mock_os_path_exists(path):
-        if path == os.path.join(MOCK_PACKAGE_DIR, 'setup.py'):
+    def mock_path_exists(path):
+        if path == MOCK_PACKAGE_DIR / 'setup.py':
             return True
         else:
-            return real_os_path_exists(path)
+            return real_path_exists(path)
 
-    monkeypatch.setattr(os.path, 'exists', mock_os_path_exists)
-    monkeypatch.setattr(sys, 'argv', ['cibuildwheel', MOCK_PACKAGE_DIR])
+    monkeypatch.setattr(Path, 'exists', mock_path_exists)
+    monkeypatch.setattr(sys, 'argv', ['cibuildwheel', str(MOCK_PACKAGE_DIR)])
 
 
 @pytest.fixture(params=['linux', 'macos', 'windows'])
diff --git a/unit_test/main_tests/main_options_test.py b/unit_test/main_tests/main_options_test.py
index 633e9cc5..14252e67 100644
--- a/unit_test/main_tests/main_options_test.py
+++ b/unit_test/main_tests/main_options_test.py
@@ -1,5 +1,6 @@
 import sys
 from fnmatch import fnmatch
+from pathlib import Path
 
 import pytest
 
@@ -12,9 +13,9 @@ from cibuildwheel.util import BuildSelector
 
 
 def test_output_dir(platform, intercepted_build_args, monkeypatch):
-    OUTPUT_DIR = 'some_output_dir'
+    OUTPUT_DIR = Path('some_output_dir')
 
-    monkeypatch.setenv('CIBW_OUTPUT_DIR', OUTPUT_DIR)
+    monkeypatch.setenv('CIBW_OUTPUT_DIR', str(OUTPUT_DIR))
 
     main()
 
@@ -24,14 +25,14 @@ def test_output_dir(platform, intercepted_build_args, monkeypatch):
 def test_output_dir_default(platform, intercepted_build_args, monkeypatch):
     main()
 
-    assert intercepted_build_args.args[0].output_dir == 'wheelhouse'
+    assert intercepted_build_args.args[0].output_dir == Path('wheelhouse')
 
 
 @pytest.mark.parametrize('also_set_environment', [False, True])
 def test_output_dir_argument(also_set_environment, platform, intercepted_build_args, monkeypatch):
-    OUTPUT_DIR = 'some_output_dir'
+    OUTPUT_DIR = Path('some_output_dir')
 
-    monkeypatch.setattr(sys, 'argv', sys.argv + ['--output-dir', OUTPUT_DIR])
+    monkeypatch.setattr(sys, 'argv', sys.argv + ['--output-dir', str(OUTPUT_DIR)])
     if also_set_environment:
         monkeypatch.setenv('CIBW_OUTPUT_DIR', 'not_this_output_dir')