--- a/testing/vcttesting/docker.py
+++ b/testing/vcttesting/docker.py
@@ -42,16 +42,17 @@ from coverage.data import CoverageData
 from .util import (
     limited_threadpoolexecutor,
     wait_for_amqp,
     wait_for_http,
     wait_for_ssh,
 )
 from .vctutil import (
     get_and_write_vct_node,
+    hg_executable,
 )
 
 
 HERE = os.path.abspath(os.path.dirname(__file__))
 DOCKER_DIR = os.path.normpath(os.path.join(HERE, '..', 'docker'))
 ROOT = os.path.normpath(os.path.join(HERE, '..', '..'))
 
 
@@ -255,20 +256,19 @@ class Docker(object):
         except requests.exceptions.RequestException:
             return False
 
     def _get_vct_files(self):
         """Obtain all the files in the version-control-tools repo.
 
         Returns a dict of relpath to full path.
         """
-        hg = os.path.join(ROOT, 'venv', 'bin', 'hg')
         env = dict(os.environ)
         env['HGRCPATH'] = '/dev/null'
-        args = [hg, '-R', '.', 'locate']
+        args = [hg_executable(), '-R', '.', 'locate']
         with open(os.devnull, 'wb') as null:
             files = subprocess.check_output(
                 args, env=env, cwd=ROOT, stderr=null).splitlines()
 
         # Add files from the nested reviewboard-fork repo.
         fork_path = os.path.join(ROOT, 'reviewboard-fork')
         if os.path.exists(fork_path):
             with open(os.devnull, 'wb') as null:

--- a/testing/vcttesting/vctutil.py
+++ b/testing/vcttesting/vctutil.py
@@ -1,26 +1,41 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 from __future__ import absolute_import, unicode_literals
 
 import os
 import subprocess
+import sys
 
 
 HERE = os.path.abspath(os.path.dirname(__file__))
 ROOT = os.path.normpath(os.path.join(HERE, '..', '..'))
 
 
+def hg_executable():
+    if 'VIRTUAL_ENV' in os.environ:
+        venv = os.environ['VIRTUAL_ENV']
+    # Virtualenv activated by Python itself, not from shell.
+    elif hasattr(sys, 'real_prefix'):
+        venv = sys.prefix
+    else:
+        venv = os.path.join(ROOT, 'venv')
+
+    if os.name == 'nt':
+        return os.path.join(venv, 'Scripts', 'hg.exe')
+    else:
+        return os.path.join(venv, 'bin', 'hg')
+
+
 def get_and_write_vct_node():
-    hg = os.path.join(os.environ['VIRTUAL_ENV'], 'bin', 'hg')
     env = dict(os.environ)
     env['HGRCPATH'] = '/dev/null'
-    args = [hg, '-R', ROOT, 'log', '-r', '.', '-T', '{node|short}']
+    args = [hg_executable(), '-R', ROOT, 'log', '-r', '.', '-T', '{node|short}']
     with open(os.devnull, 'wb') as null:
         node = subprocess.check_output(args, env=env, cwd='/', stderr=null)
 
     with open(os.path.join(ROOT, '.vctnode'), 'wb') as fh:
         fh.write(node)
 
     return node