--- a/vcssync/mozvcssync/cli.py
+++ b/vcssync/mozvcssync/cli.py
@@ -221,16 +221,18 @@ def overlay_hg_repos_cli():
                         help='URL of repository where changesets will be '
                              'overlayed')
     parser.add_argument('dest_repo_path',
                         help='Local path to clone of <dest_repo_url>')
     parser.add_argument('--source_revs',
                         help='Revset describing changesets to overlay')
     parser.add_argument('--result-push-url',
                         help='URL where to push the overlayed result')
+    parser.add_argument('--noncontiguous', action='store_true',
+                        help='Allow a non-contiguous source_revs')
 
     args = parser.parse_args()
 
     if args.hg:
         hglib.HGPATH = args.hg
 
     configure_logging()
 
@@ -241,17 +243,18 @@ def overlay_hg_repos_cli():
         attempt += 1
         try:
             overlay_hg_repos(
                 args.source_repo_url,
                 args.dest_repo_url,
                 args.dest_repo_path,
                 source_rev=args.source_revs,
                 dest_prefix=args.into,
-                result_push_url=args.result_push_url)
+                result_push_url=args.result_push_url,
+                noncontiguous=args.noncontiguous)
             sys.exit(0)
         except PushRaceError:
             logger.warn('likely push race on attempt %d/%d' % (
                 attempt, MAX_ATTEMPTS))
             if attempt < MAX_ATTEMPTS:
                 logger.warn('retrying immediately...')
         except PushRemoteFail:
             logger.warn('push failed by remote on attempt %d/%d' % (

--- a/vcssync/mozvcssync/overlay.py
+++ b/vcssync/mozvcssync/overlay.py
@@ -23,17 +23,17 @@ class PushRaceError(Exception):
 
 
 class PushRemoteFail(Exception):
     """Raised when a push fails due to an error on the remote."""
 
 
 def overlay_hg_repos(source_repo_url, dest_repo_url, dest_repo_path,
                      dest_prefix, source_rev=None, dest_rev='tip',
-                     result_push_url=None):
+                     result_push_url=None, noncontiguous=False):
     """Overlay changesets from an hg repo into a sub-directory of another.
 
     This function will take changesets from the Mercurial repo
     at ``source_url`` and apply them to the Mercurial repo at
     ``dest_repo_url``, rewriting file paths so they are stored in
     the directory ``dest_prefix`` of the destination repository.
 
     A copy of ``dest_repo_url`` is managed at ``dest_repo_path``,
@@ -90,16 +90,20 @@ def overlay_hg_repos(source_repo_url, de
 
         # The destination revision is now present locally. Commence the overlay!
         args = [
             b'overlay',
             source_repo_url,
             b'--into', dest_prefix,
             b'-d', dest_node,
         ]
+
+        if noncontiguous:
+            args.append('--noncontiguous')
+
         if source_rev:
             args.append(source_rev)
 
         logger.warn('commencing overlay of %s' % source_repo_url)
         run_hg(logger, hrepo, args)
 
         new_tip = hrepo[b'tip']
         if new_tip.rev() == old_tip.rev():

--- a/vcssync/mozvcssync/servo.py
+++ b/vcssync/mozvcssync/servo.py
@@ -313,17 +313,19 @@ def overlay_cli():
     if args.result_push_url:
         overlay_hg_repos.extend(['--result-push-url', args.result_push_url])
     if args.hg:
         overlay_hg_repos.extend(['--hg', args.hg])
 
     # Exclude pull requests generated by servo-backout-pr
     if os.getenv('BACKOUT_AUTHOR'):
         overlay_hg_repos.extend([
-            '--source_revs', 'not author("%s")' % os.getenv('BACKOUT_AUTHOR')])
+            '--source_revs', 'not author("%s")' % os.getenv('BACKOUT_AUTHOR'),
+            '--noncontiguous',
+        ])
 
     try:
         subprocess.check_call(overlay_hg_repos)
     except Exception as e:
         # A stack trace from here is not useful.
         logger.error('abort: %s' % str(e))
         sys.exit(1)