diff --git a/fawltydeps/packages.py b/fawltydeps/packages.py
index 4a17c6e1..438d1363 100644
--- a/fawltydeps/packages.py
+++ b/fawltydeps/packages.py
@@ -1,6 +1,7 @@
 """Encapsulate the lookup of packages and their provided import names."""
 
 import logging
+import os
 import platform
 import subprocess
 import sys
@@ -346,6 +347,15 @@ def find_package_dirs(cls, path: Path) -> Iterator[Path]:
             if found:
                 return
 
+        # Check for packages on Windows
+        if platform.system() == "Windows":
+            for site_packages in path.glob(os.path.join("Lib", "site-packages")):
+                if site_packages.is_dir():
+                    yield site_packages
+                    found = True
+            if found:
+                return
+
         # Given path is not a python environment, but it might be _inside_ one.
         # Try again with parent directory
         if path.parent != path:
diff --git a/fawltydeps/types.py b/fawltydeps/types.py
index 45f6aeb8..788ce5d8 100644
--- a/fawltydeps/types.py
+++ b/fawltydeps/types.py
@@ -1,5 +1,7 @@
 """Common types used across FawltyDeps."""
 
+import os
+import platform
 import sys
 from abc import ABC, abstractmethod
 from dataclasses import asdict, dataclass, field, replace
@@ -155,6 +157,12 @@ def __post_init__(self) -> None:
         elif self.path.match("__pypackages__/?.*/lib"):
             return  # also ok
 
+        # Support Windows projects
+        if platform.system() == "Windows" and self.path.match(
+            os.path.join("Lib", "site-packages")
+        ):
+            return  # also ok
+
         raise ValueError(f"{self.path} is not a valid dir for Python packages!")
 
     def render(self, detailed: bool) -> str:
diff --git a/pyproject.toml b/pyproject.toml
index c6b18ded..a9850dd3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -118,7 +118,7 @@ profile = "black"
 main.jobs = 4
 main.py-version = "3.7"
 reports.output-format = "colorized"
-"messages control".disable = "fixme,logging-fstring-interpolation,unspecified-encoding,too-few-public-methods,consider-using-in,duplicate-code"
+"messages control".disable = "fixme,logging-fstring-interpolation,unspecified-encoding,too-few-public-methods,consider-using-in,duplicate-code,too-many-locals,too-many-branches"
 
 [tool.mypy]
 files = ['*.py', 'fawltydeps/*.py', 'tests/*.py']
diff --git a/tests/conftest.py b/tests/conftest.py
index dd041ec7..515b749b 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,4 +1,5 @@
 """Fixtures for tests"""
+import platform
 import sys
 import venv
 from pathlib import Path
@@ -54,7 +55,13 @@ def create_one_fake_venv(
 
         # Create fake packages
         major, minor = py_version
-        site_dir = venv_dir / f"lib/python{major}.{minor}/site-packages"
+
+        def _env_site_packages():
+            if platform.system() == "Windows":
+                return venv_dir / "Lib" / "site-packages"
+            return venv_dir / "lib" / f"python{major}.{minor}" / "site-packages"
+
+        site_dir = _env_site_packages()
         assert site_dir.is_dir()
         for package_name, import_names in fake_packages.items():
             # Create just enough files under site_dir to fool importlib_metadata
diff --git a/tests/test_cmdline.py b/tests/test_cmdline.py
index 3e5c0072..f60a7d85 100644
--- a/tests/test_cmdline.py
+++ b/tests/test_cmdline.py
@@ -452,7 +452,9 @@ def test_list_sources__in_varied_project__lists_all_files(fake_project):
             "pyproject.toml",
             "setup.py",
             "setup.cfg",
-            f"my_venv/lib/python{major}.{minor}/site-packages",
+            os.path.join("my_venv", "Lib", "site-packages")
+            if platform.system() == "Windows"
+            else f"my_venv/lib/python{major}.{minor}/site-packages",
         ]
     ]
     assert_unordered_equivalence(output.splitlines()[:-2], expect)
@@ -497,8 +499,19 @@ def test_list_sources_detailed__in_varied_project__lists_all_files(fake_project)
     ]
     major, minor = sys.version_info[:2]
     expect_pyenv_lines = [
-        f"  {tmp_path}/my_venv/lib/python{major}.{minor}/site-packages "
-        + "(as a source of Python packages)",
+        (
+            "  " + str(tmp_path / "my_venv" / "Lib" / "site-packages")
+            if platform.system() == "Windows"
+            else "  "
+            + str(
+                tmp_path
+                / "my_venv"
+                / "lib"
+                / f"python{major}.{minor}"
+                / "site-packages"
+            )
+        )
+        + " (as a source of Python packages)",
     ]
     expect = [
         "Sources of Python code:",
@@ -688,7 +701,11 @@ def test_check_json__simple_project__can_report_both_undeclared_and_unused(
             },
             {
                 "source_type": "PyEnvSource",
-                "path": f"{tmp_path}/my_venv/lib/python{major}.{minor}/site-packages",
+                "path": (
+                    f"{tmp_path / 'my_venv' / 'Lib' / 'site-packages'}"
+                    if platform.system() == "Windows"
+                    else f"{tmp_path}/my_venv/lib/python{major}.{minor}/site-packages"
+                ),
             },
         ],
         "imports": [
diff --git a/tests/test_local_env.py b/tests/test_local_env.py
index d372cd15..92f5a9ed 100644
--- a/tests/test_local_env.py
+++ b/tests/test_local_env.py
@@ -37,6 +37,14 @@
     f"__pypackages__/{major}.{minor}/lib",
 ]
 
+# When the user gives us a --pyenv arg that points to a Python virtualenv
+# on Windows, what are the the possible paths inside that Python environment
+# that they might point at (and that we should accept)?
+windows_subdirs = [
+    "",
+    "Lib",
+    os.path.join("Lib", "site-packages"),
+]
 
 @pytest.mark.parametrize(
     "subdir", [pytest.param(d, id=f"venv:{d}") for d in env_subdirs]
@@ -128,7 +136,11 @@ def test_local_env__default_venv__contains_pip(tmp_path):
     # "pip" package is installed, and that it provides a "pip" import name.
     venv.create(tmp_path, with_pip=True)
     lpl = LocalPackageResolver(pyenv_sources(tmp_path))
-    expect_location = tmp_path / f"lib/python{major}.{minor}/site-packages"
+    expect_location = (
+        tmp_path / "Lib" / "site-packages"
+        if platform.system() == "Windows"
+        else tmp_path / f"lib/python{major}.{minor}/site-packages"
+    )
     assert "pip" in lpl.packages
     pip = lpl.packages["pip"]
     assert pip.package_name == "pip"