diff --git a/contrib/packaging/hgpackaging/wix.py b/contrib/packaging/hgpackaging/wix.py
--- a/contrib/packaging/hgpackaging/wix.py
+++ b/contrib/packaging/hgpackaging/wix.py
@@ -12,6 +12,7 @@
 import re
 import subprocess
 import tempfile
+import typing
 import xml.dom.minidom
 
 from .downloads import (
@@ -178,7 +179,8 @@
 
 def build_installer(source_dir: pathlib.Path, python_exe: pathlib.Path,
                     msi_name='mercurial', version=None, post_build_fn=None,
-                    extra_prebuild_script=None):
+                    extra_prebuild_script=None,
+                    extra_wxs:typing.Optional[typing.Dict[str,str]]=None):
     """Build a WiX MSI installer.
 
     ``source_dir`` is the path to the Mercurial source tree to use.
@@ -190,6 +192,7 @@
     Mercurial but before invoking WiX. It can be used to e.g. facilitate
     signing. It is passed the paths to the Mercurial source, build, and
     dist directories and the resolved Mercurial version.
+    ``extra_wxs`` is a dict of {wxs_name: working_dir_for_wxs_build}.
     """
     arch = 'x64' if r'\x64' in os.environ.get('LIB', '') else 'x86'
 
@@ -231,6 +234,9 @@
         wxs_source_dir = source_dir / rel_path
         run_candle(wix_path, build_dir, wxs, wxs_source_dir, defines=defines)
 
+    for source, rel_path in sorted((extra_wxs or {}).items()):
+        run_candle(wix_path, build_dir, source, rel_path, defines=defines)
+
     # candle.exe doesn't like when we have an open handle on the file.
     # So use TemporaryDirectory() instead of NamedTemporaryFile().
     with tempfile.TemporaryDirectory() as td:
@@ -265,6 +271,11 @@
         assert source.endswith('.wxs')
         args.append(str(build_dir / ('%s.wixobj' % source[:-4])))
 
+    for source, rel_path in sorted((extra_wxs or {}).items()):
+        assert source.endswith('.wxs')
+        source = os.path.basename(source)
+        args.append(str(build_dir / ('%s.wixobj' % source[:-4])))
+
     args.extend([
         str(build_dir / 'library.wixobj'),
         str(build_dir / 'mercurial.wixobj'),
@@ -282,7 +293,8 @@
 def build_signed_installer(source_dir: pathlib.Path, python_exe: pathlib.Path,
                            name: str, version=None, subject_name=None,
                            cert_path=None, cert_password=None,
-                           timestamp_url=None, extra_prebuild_script=None):
+                           timestamp_url=None, extra_prebuild_script=None,
+                           extra_wxs=None):
     """Build an installer with signed executables."""
 
     post_build_fn = make_post_build_signing_fn(
@@ -295,7 +307,8 @@
     info = build_installer(source_dir, python_exe=python_exe,
                            msi_name=name.lower(), version=version,
                            post_build_fn=post_build_fn,
-                           extra_prebuild_script=extra_prebuild_script)
+                           extra_prebuild_script=extra_prebuild_script,
+                           extra_wxs=extra_wxs)
 
     description = '%s %s' % (name, version)
 
diff --git a/contrib/packaging/wix/build.py b/contrib/packaging/wix/build.py
--- a/contrib/packaging/wix/build.py
+++ b/contrib/packaging/wix/build.py
@@ -36,6 +36,8 @@
                         help='Version string to use')
     parser.add_argument('--extra-prebuild-script',
                         help='Extra script to run after creating virtualenv.')
+    parser.add_argument('--extra-wxs', 
+                        help='CSV of path_to_wxs_file=working_dir_for_wxs_file')
 
     args = parser.parse_args()
 
@@ -58,6 +60,9 @@
 
     if args.extra_prebuild_script:
         kwargs['extra_prebuild_script'] = args.extra_prebuild_script
+    if args.extra_wxs:
+        kwargs['extra_wxs'] = dict(
+            thing.split("=") for thing in args.extra_wxs.split(','))
 
     if args.sign_sn or args.sign_cert:
         fn = build_signed_installer