diff --git a/contrib/automation/hgautomation/windows.py b/contrib/automation/hgautomation/windows.py
--- a/contrib/automation/hgautomation/windows.py
+++ b/contrib/automation/hgautomation/windows.py
@@ -71,7 +71,7 @@
 BUILD_INNO = r'''
 Set-Location C:\hgdev\src
 $python = "C:\hgdev\python27-{arch}\python.exe"
-C:\hgdev\python37-x64\python.exe contrib\packaging\inno\build.py --python $python
+C:\hgdev\python37-x64\python.exe contrib\packaging\packaging.py inno --python $python
 if ($LASTEXITCODE -ne 0) {{
     throw "process exited non-0: $LASTEXITCODE"
 }}
@@ -88,7 +88,7 @@
 BUILD_WIX = r'''
 Set-Location C:\hgdev\src
 $python = "C:\hgdev\python27-{arch}\python.exe"
-C:\hgdev\python37-x64\python.exe contrib\packaging\wix\build.py --python $python {extra_args}
+C:\hgdev\python37-x64\python.exe contrib\packaging\packaging.py wix --python $python {extra_args}
 if ($LASTEXITCODE -ne 0) {{
     throw "process exited non-0: $LASTEXITCODE"
 }}
diff --git a/contrib/packaging/hgpackaging/cli.py b/contrib/packaging/hgpackaging/cli.py
new file mode 100644
--- /dev/null
+++ b/contrib/packaging/hgpackaging/cli.py
@@ -0,0 +1,153 @@
+# cli.py - Command line interface for automation
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc@gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+# no-check-code because Python 3 native.
+
+import argparse
+import os
+import pathlib
+
+from . import (
+    inno,
+    wix,
+)
+
+HERE = pathlib.Path(os.path.abspath(os.path.dirname(__file__)))
+SOURCE_DIR = HERE.parent.parent.parent
+
+
+def build_inno(python=None, iscc=None, version=None):
+    if not os.path.isabs(python):
+        raise Exception("--python arg must be an absolute path")
+
+    if iscc:
+        iscc = pathlib.Path(iscc)
+    else:
+        iscc = (
+            pathlib.Path(os.environ["ProgramFiles(x86)"])
+            / "Inno Setup 5"
+            / "ISCC.exe"
+        )
+
+    build_dir = SOURCE_DIR / "build"
+
+    inno.build(
+        SOURCE_DIR, build_dir, pathlib.Path(python), iscc, version=version,
+    )
+
+
+def build_wix(
+    name=None,
+    python=None,
+    version=None,
+    sign_sn=None,
+    sign_cert=None,
+    sign_password=None,
+    sign_timestamp_url=None,
+    extra_packages_script=None,
+    extra_wxs=None,
+    extra_features=None,
+):
+    fn = wix.build_installer
+    kwargs = {
+        "source_dir": SOURCE_DIR,
+        "python_exe": pathlib.Path(python),
+        "version": version,
+    }
+
+    if not os.path.isabs(python):
+        raise Exception("--python arg must be an absolute path")
+
+    if extra_packages_script:
+        kwargs["extra_packages_script"] = extra_packages_script
+    if extra_wxs:
+        kwargs["extra_wxs"] = dict(
+            thing.split("=") for thing in extra_wxs.split(",")
+        )
+    if extra_features:
+        kwargs["extra_features"] = extra_features.split(",")
+
+    if sign_sn or sign_cert:
+        fn = wix.build_signed_installer
+        kwargs["name"] = name
+        kwargs["subject_name"] = sign_sn
+        kwargs["cert_path"] = sign_cert
+        kwargs["cert_password"] = sign_password
+        kwargs["timestamp_url"] = sign_timestamp_url
+
+    fn(**kwargs)
+
+
+def get_parser():
+    parser = argparse.ArgumentParser()
+
+    subparsers = parser.add_subparsers()
+
+    sp = subparsers.add_parser("inno", help="Build Inno Setup installer")
+    sp.add_argument("--python", required=True, help="path to python.exe to use")
+    sp.add_argument("--iscc", help="path to iscc.exe to use")
+    sp.add_argument(
+        "--version",
+        help="Mercurial version string to use "
+        "(detected from __version__.py if not defined",
+    )
+    sp.set_defaults(func=build_inno)
+
+    sp = subparsers.add_parser(
+        "wix", help="Build Windows installer with WiX Toolset"
+    )
+    sp.add_argument("--name", help="Application name", default="Mercurial")
+    sp.add_argument(
+        "--python", help="Path to Python executable to use", required=True
+    )
+    sp.add_argument(
+        "--sign-sn",
+        help="Subject name (or fragment thereof) of certificate "
+        "to use for signing",
+    )
+    sp.add_argument(
+        "--sign-cert", help="Path to certificate to use for signing"
+    )
+    sp.add_argument("--sign-password", help="Password for signing certificate")
+    sp.add_argument(
+        "--sign-timestamp-url",
+        help="URL of timestamp server to use for signing",
+    )
+    sp.add_argument("--version", help="Version string to use")
+    sp.add_argument(
+        "--extra-packages-script",
+        help=(
+            "Script to execute to include extra packages in " "py2exe binary."
+        ),
+    )
+    sp.add_argument(
+        "--extra-wxs", help="CSV of path_to_wxs_file=working_dir_for_wxs_file"
+    )
+    sp.add_argument(
+        "--extra-features",
+        help=(
+            "CSV of extra feature names to include "
+            "in the installer from the extra wxs files"
+        ),
+    )
+    sp.set_defaults(func=build_wix)
+
+    return parser
+
+
+def main():
+    parser = get_parser()
+    args = parser.parse_args()
+
+    if not hasattr(args, "func"):
+        parser.print_help()
+        return
+
+    kwargs = dict(vars(args))
+    del kwargs["func"]
+
+    args.func(**kwargs)
diff --git a/contrib/packaging/inno/build.py b/contrib/packaging/inno/build.py
deleted file mode 100755
--- a/contrib/packaging/inno/build.py
+++ /dev/null
@@ -1,60 +0,0 @@
-#!/usr/bin/env python3
-# build.py - Inno installer build script.
-#
-# Copyright 2019 Gregory Szorc <gregory.szorc@gmail.com>
-#
-# This software may be used and distributed according to the terms of the
-# GNU General Public License version 2 or any later version.
-
-# This script automates the building of the Inno MSI installer for Mercurial.
-
-# no-check-code because Python 3 native.
-
-import argparse
-import os
-import pathlib
-import sys
-
-
-if __name__ == '__main__':
-    parser = argparse.ArgumentParser()
-
-    parser.add_argument(
-        '--python', required=True, help='path to python.exe to use'
-    )
-    parser.add_argument('--iscc', help='path to iscc.exe to use')
-    parser.add_argument(
-        '--version',
-        help='Mercurial version string to use '
-        '(detected from __version__.py if not defined',
-    )
-
-    args = parser.parse_args()
-
-    if not os.path.isabs(args.python):
-        raise Exception('--python arg must be an absolute path')
-
-    if args.iscc:
-        iscc = pathlib.Path(args.iscc)
-    else:
-        iscc = (
-            pathlib.Path(os.environ['ProgramFiles(x86)'])
-            / 'Inno Setup 5'
-            / 'ISCC.exe'
-        )
-
-    here = pathlib.Path(os.path.abspath(os.path.dirname(__file__)))
-    source_dir = here.parent.parent.parent
-    build_dir = source_dir / 'build'
-
-    sys.path.insert(0, str(source_dir / 'contrib' / 'packaging'))
-
-    from hgpackaging.inno import build
-
-    build(
-        source_dir,
-        build_dir,
-        pathlib.Path(args.python),
-        iscc,
-        version=args.version,
-    )
diff --git a/contrib/packaging/inno/readme.rst b/contrib/packaging/inno/readme.rst
--- a/contrib/packaging/inno/readme.rst
+++ b/contrib/packaging/inno/readme.rst
@@ -11,12 +11,12 @@
 * Inno Setup (http://jrsoftware.org/isdl.php) version 5.4 or newer.
   Be sure to install the optional Inno Setup Preprocessor feature,
   which is required.
-* Python 3.5+ (to run the ``build.py`` script)
+* Python 3.5+ (to run the ``packaging.py`` script)
 
 Building
 ========
 
-The ``build.py`` script automates the process of producing an
+The ``packaging.py`` script automates the process of producing an
 Inno installer. It manages fetching and configuring the
 non-system dependencies (such as py2exe, gettext, and various
 Python packages).
@@ -31,11 +31,11 @@
 From the prompt, change to the Mercurial source directory. e.g.
 ``cd c:\src\hg``.
 
-Next, invoke ``build.py`` to produce an Inno installer. You will
+Next, invoke ``packaging.py`` to produce an Inno installer. You will
 need to supply the path to the Python interpreter to use.::
 
-   $ python3.exe contrib\packaging\inno\build.py \
-       --python c:\python27\python.exe
+   $ python3.exe contrib\packaging\packaging.py \
+       inno --python c:\python27\python.exe
 
 .. note::
 
@@ -49,13 +49,13 @@
 and an installer placed in the ``dist`` sub-directory. The final
 line of output should print the name of the generated installer.
 
-Additional options may be configured. Run ``build.py --help`` to
-see a list of program flags.
+Additional options may be configured. Run
+``packaging.py inno --help`` to see a list of program flags.
 
 MinGW
 =====
 
 It is theoretically possible to generate an installer that uses
-MinGW. This isn't well tested and ``build.py`` and may properly
+MinGW. This isn't well tested and ``packaging.py`` and may properly
 support it. See old versions of this file in version control for
 potentially useful hints as to how to achieve this.
diff --git a/contrib/packaging/packaging.py b/contrib/packaging/packaging.py
new file mode 100755
--- /dev/null
+++ b/contrib/packaging/packaging.py
@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+#
+# packaging.py - Mercurial packaging functionality
+#
+# Copyright 2019 Gregory Szorc <gregory.szorc@gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+import os
+import pathlib
+import subprocess
+import sys
+import venv
+
+
+HERE = pathlib.Path(os.path.abspath(__file__)).parent
+REQUIREMENTS_TXT = HERE / "requirements.txt"
+SOURCE_DIR = HERE.parent.parent
+VENV = SOURCE_DIR / "build" / "venv-packaging"
+
+
+def bootstrap():
+    venv_created = not VENV.exists()
+
+    VENV.parent.mkdir(exist_ok=True)
+
+    venv.create(VENV, with_pip=True)
+
+    if os.name == "nt":
+        venv_bin = VENV / "Scripts"
+        pip = venv_bin / "pip.exe"
+        python = venv_bin / "python.exe"
+    else:
+        venv_bin = VENV / "bin"
+        pip = venv_bin / "pip"
+        python = venv_bin / "python"
+
+    args = [
+        str(pip),
+        "install",
+        "-r",
+        str(REQUIREMENTS_TXT),
+        "--disable-pip-version-check",
+    ]
+
+    if not venv_created:
+        args.append("-q")
+
+    subprocess.run(args, check=True)
+
+    os.environ["HGPACKAGING_BOOTSTRAPPED"] = "1"
+    os.environ["PATH"] = "%s%s%s" % (venv_bin, os.pathsep, os.environ["PATH"])
+
+    subprocess.run([str(python), __file__] + sys.argv[1:], check=True)
+
+
+def run():
+    import hgpackaging.cli as cli
+
+    # Need to strip off main Python executable.
+    cli.main()
+
+
+if __name__ == "__main__":
+    try:
+        if "HGPACKAGING_BOOTSTRAPPED" not in os.environ:
+            bootstrap()
+        else:
+            run()
+    except subprocess.CalledProcessError as e:
+        sys.exit(e.returncode)
+    except KeyboardInterrupt:
+        sys.exit(1)
diff --git a/contrib/packaging/requirements.txt b/contrib/packaging/requirements.txt
new file mode 100644
--- /dev/null
+++ b/contrib/packaging/requirements.txt
@@ -0,0 +1,39 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --generate-hashes --output-file=contrib/packaging/requirements.txt contrib/packaging/requirements.txt.in
+#
+jinja2==2.10.3 \
+    --hash=sha256:74320bb91f31270f9551d46522e33af46a80c3d619f4a4bf42b3164d30b5911f \
+    --hash=sha256:9fe95f19286cfefaa917656583d020be14e7859c6b0252588391e47db34527de
+markupsafe==1.1.1 \
+    --hash=sha256:00bc623926325b26bb9605ae9eae8a215691f33cae5df11ca5424f06f2d1f473 \
+    --hash=sha256:09027a7803a62ca78792ad89403b1b7a73a01c8cb65909cd876f7fcebd79b161 \
+    --hash=sha256:09c4b7f37d6c648cb13f9230d847adf22f8171b1ccc4d5682398e77f40309235 \
+    --hash=sha256:1027c282dad077d0bae18be6794e6b6b8c91d58ed8a8d89a89d59693b9131db5 \
+    --hash=sha256:24982cc2533820871eba85ba648cd53d8623687ff11cbb805be4ff7b4c971aff \
+    --hash=sha256:29872e92839765e546828bb7754a68c418d927cd064fd4708fab9fe9c8bb116b \
+    --hash=sha256:43a55c2930bbc139570ac2452adf3d70cdbb3cfe5912c71cdce1c2c6bbd9c5d1 \
+    --hash=sha256:46c99d2de99945ec5cb54f23c8cd5689f6d7177305ebff350a58ce5f8de1669e \
+    --hash=sha256:500d4957e52ddc3351cabf489e79c91c17f6e0899158447047588650b5e69183 \
+    --hash=sha256:535f6fc4d397c1563d08b88e485c3496cf5784e927af890fb3c3aac7f933ec66 \
+    --hash=sha256:62fe6c95e3ec8a7fad637b7f3d372c15ec1caa01ab47926cfdf7a75b40e0eac1 \
+    --hash=sha256:6dd73240d2af64df90aa7c4e7481e23825ea70af4b4922f8ede5b9e35f78a3b1 \
+    --hash=sha256:717ba8fe3ae9cc0006d7c451f0bb265ee07739daf76355d06366154ee68d221e \
+    --hash=sha256:79855e1c5b8da654cf486b830bd42c06e8780cea587384cf6545b7d9ac013a0b \
+    --hash=sha256:7c1699dfe0cf8ff607dbdcc1e9b9af1755371f92a68f706051cc8c37d447c905 \
+    --hash=sha256:88e5fcfb52ee7b911e8bb6d6aa2fd21fbecc674eadd44118a9cc3863f938e735 \
+    --hash=sha256:8defac2f2ccd6805ebf65f5eeb132adcf2ab57aa11fdf4c0dd5169a004710e7d \
+    --hash=sha256:98c7086708b163d425c67c7a91bad6e466bb99d797aa64f965e9d25c12111a5e \
+    --hash=sha256:9add70b36c5666a2ed02b43b335fe19002ee5235efd4b8a89bfcf9005bebac0d \
+    --hash=sha256:9bf40443012702a1d2070043cb6291650a0841ece432556f784f004937f0f32c \
+    --hash=sha256:ade5e387d2ad0d7ebf59146cc00c8044acbd863725f887353a10df825fc8ae21 \
+    --hash=sha256:b00c1de48212e4cc9603895652c5c410df699856a2853135b3967591e4beebc2 \
+    --hash=sha256:b1282f8c00509d99fef04d8ba936b156d419be841854fe901d8ae224c59f0be5 \
+    --hash=sha256:b2051432115498d3562c084a49bba65d97cf251f5a331c64a12ee7e04dacc51b \
+    --hash=sha256:ba59edeaa2fc6114428f1637ffff42da1e311e29382d81b339c1817d37ec93c6 \
+    --hash=sha256:c8716a48d94b06bb3b2524c2b77e055fb313aeb4ea620c8dd03a105574ba704f \
+    --hash=sha256:cd5df75523866410809ca100dc9681e301e3c27567cf498077e8551b6d20e42f \
+    --hash=sha256:e249096428b3ae81b08327a63a485ad0878de3fb939049038579ac0ef61e17e7 \
+    # via jinja2
diff --git a/contrib/packaging/requirements.txt.in b/contrib/packaging/requirements.txt.in
new file mode 100644
--- /dev/null
+++ b/contrib/packaging/requirements.txt.in
@@ -0,0 +1 @@
+jinja2
diff --git a/contrib/packaging/wix/build.py b/contrib/packaging/wix/build.py
deleted file mode 100755
--- a/contrib/packaging/wix/build.py
+++ /dev/null
@@ -1,96 +0,0 @@
-#!/usr/bin/env python3
-# Copyright 2019 Gregory Szorc <gregory.szorc@gmail.com>
-#
-# This software may be used and distributed according to the terms of the
-# GNU General Public License version 2 or any later version.
-
-# no-check-code because Python 3 native.
-
-"""Code to build Mercurial WiX installer."""
-
-import argparse
-import os
-import pathlib
-import sys
-
-
-if __name__ == '__main__':
-    parser = argparse.ArgumentParser()
-
-    parser.add_argument('--name', help='Application name', default='Mercurial')
-    parser.add_argument(
-        '--python', help='Path to Python executable to use', required=True
-    )
-    parser.add_argument(
-        '--sign-sn',
-        help='Subject name (or fragment thereof) of certificate '
-        'to use for signing',
-    )
-    parser.add_argument(
-        '--sign-cert', help='Path to certificate to use for signing'
-    )
-    parser.add_argument(
-        '--sign-password', help='Password for signing certificate'
-    )
-    parser.add_argument(
-        '--sign-timestamp-url',
-        help='URL of timestamp server to use for signing',
-    )
-    parser.add_argument('--version', help='Version string to use')
-    parser.add_argument(
-        '--extra-packages-script',
-        help=(
-            'Script to execute to include extra packages in ' 'py2exe binary.'
-        ),
-    )
-    parser.add_argument(
-        '--extra-wxs', help='CSV of path_to_wxs_file=working_dir_for_wxs_file'
-    )
-    parser.add_argument(
-        '--extra-features',
-        help=(
-            'CSV of extra feature names to include '
-            'in the installer from the extra wxs files'
-        ),
-    )
-
-    args = parser.parse_args()
-
-    here = pathlib.Path(os.path.abspath(os.path.dirname(__file__)))
-    source_dir = here.parent.parent.parent
-
-    sys.path.insert(0, str(source_dir / 'contrib' / 'packaging'))
-
-    from hgpackaging.wix import (
-        build_installer,
-        build_signed_installer,
-    )
-
-    fn = build_installer
-    kwargs = {
-        'source_dir': source_dir,
-        'python_exe': pathlib.Path(args.python),
-        'version': args.version,
-    }
-
-    if not os.path.isabs(args.python):
-        raise Exception('--python arg must be an absolute path')
-
-    if args.extra_packages_script:
-        kwargs['extra_packages_script'] = args.extra_packages_script
-    if args.extra_wxs:
-        kwargs['extra_wxs'] = dict(
-            thing.split("=") for thing in args.extra_wxs.split(',')
-        )
-    if args.extra_features:
-        kwargs['extra_features'] = args.extra_features.split(',')
-
-    if args.sign_sn or args.sign_cert:
-        fn = build_signed_installer
-        kwargs['name'] = args.name
-        kwargs['subject_name'] = args.sign_sn
-        kwargs['cert_path'] = args.sign_cert
-        kwargs['cert_password'] = args.sign_password
-        kwargs['timestamp_url'] = args.sign_timestamp_url
-
-    fn(**kwargs)
diff --git a/contrib/packaging/wix/readme.rst b/contrib/packaging/wix/readme.rst
--- a/contrib/packaging/wix/readme.rst
+++ b/contrib/packaging/wix/readme.rst
@@ -18,12 +18,12 @@
 * Python 2.7 (download from https://www.python.org/downloads/)
 * Microsoft Visual C++ Compiler for Python 2.7
   (https://www.microsoft.com/en-us/download/details.aspx?id=44266)
-* Python 3.5+ (to run the ``build.py`` script)
+* Python 3.5+ (to run the ``packaging.py`` script)
 
 Building
 ========
 
-The ``build.py`` script automates the process of producing an MSI
+The ``packaging.py`` script automates the process of producing an MSI
 installer. It manages fetching and configuring non-system dependencies
 (such as py2exe, gettext, and various Python packages).
 
@@ -37,11 +37,11 @@
 From the prompt, change to the Mercurial source directory. e.g.
 ``cd c:\src\hg``.
 
-Next, invoke ``build.py`` to produce an MSI installer. You will need
+Next, invoke ``packaging.py`` to produce an MSI installer. You will need
 to supply the path to the Python interpreter to use.::
 
-   $ python3 contrib\packaging\wix\build.py \
-      --python c:\python27\python.exe
+   $ python3 contrib\packaging\packaging.py \
+      wix --python c:\python27\python.exe
 
 .. note::
 
@@ -54,8 +54,8 @@
 and an installer placed in the ``dist`` sub-directory. The final line
 of output should print the name of the generated installer.
 
-Additional options may be configured. Run ``build.py --help`` to see
-a list of program flags.
+Additional options may be configured. Run ``packaging.py wix --help`` to
+see a list of program flags.
 
 Relationship to TortoiseHG
 ==========================
diff --git a/tests/test-check-code.t b/tests/test-check-code.t
--- a/tests/test-check-code.t
+++ b/tests/test-check-code.t
@@ -21,13 +21,12 @@
   Skipping contrib/automation/hgautomation/try_server.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/windows.py it has no-che?k-code (glob)
   Skipping contrib/automation/hgautomation/winrm.py it has no-che?k-code (glob)
+  Skipping contrib/packaging/hgpackaging/cli.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/downloads.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/inno.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/py2exe.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/util.py it has no-che?k-code (glob)
   Skipping contrib/packaging/hgpackaging/wix.py it has no-che?k-code (glob)
-  Skipping contrib/packaging/inno/build.py it has no-che?k-code (glob)
-  Skipping contrib/packaging/wix/build.py it has no-che?k-code (glob)
   Skipping i18n/polib.py it has no-che?k-code (glob)
   Skipping mercurial/statprof.py it has no-che?k-code (glob)
   Skipping tests/badserverext.py it has no-che?k-code (glob)
diff --git a/tests/test-check-py3-compat.t b/tests/test-check-py3-compat.t
--- a/tests/test-check-py3-compat.t
+++ b/tests/test-check-py3-compat.t
@@ -8,6 +8,7 @@
   > -X contrib/automation/ \
   > -X contrib/packaging/hgpackaging/ \
   > -X contrib/packaging/inno/ \
+  > -X contrib/packaging/packaging.py \
   > -X contrib/packaging/wix/ \
   > -X hgdemandimport/demandimportpy2.py \
   > -X mercurial/thirdparty/cbor \