--- a/testing/mozharness/configs/unittests/win_unittest.py
+++ b/testing/mozharness/configs/unittests/win_unittest.py
@@ -21,16 +21,18 @@ config = {
         'tooltool.py': [sys.executable, 'C:/mozilla-build/tooltool.py'],
     },
     ###
     "installer_path": INSTALLER_PATH,
     "binary_path": BINARY_PATH,
     "xpcshell_name": XPCSHELL_NAME,
     "virtualenv_path": 'venv',
     "virtualenv_python_dll": os.path.join(os.path.dirname(sys.executable), "python27.dll"),
+    "virtualenv_modules": ['pywin32'],
+
     "find_links": [
         "http://pypi.pvt.build.mozilla.org/pub",
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "pip_index": False,
     "exe_suffix": EXE_SUFFIX,
     "run_file_names": {
         "mochitest": "runtests.py",