diff --git a/gitlab/lock_migrated_phabricator_tasks.py b/gitlab/lock_migrated_phabricator_tasks.py
new file mode 100755
index 0000000..5e7729e
--- /dev/null
+++ b/gitlab/lock_migrated_phabricator_tasks.py
@@ -0,0 +1,221 @@
+#!/usr/bin/env python3
+
+from __future__ import annotations
+
+import logging
+import os
+import sys
+from collections import defaultdict
+from itertools import zip_longest
+
+import click
+from phabricator import Phabricator
+
+import gitlab
+
+logger = logging.getLogger(__name__)
+
+
+def grouper(iterable, n, *, incomplete="fill", fillvalue=None):
+    "Collect data into non-overlapping fixed-length chunks or blocks"
+    # grouper('ABCDEFG', 3, fillvalue='x') --> ABC DEF Gxx
+    # grouper('ABCDEFG', 3, incomplete='strict') --> ABC DEF ValueError
+    # grouper('ABCDEFG', 3, incomplete='ignore') --> ABC DEF
+    args = [iter(iterable)] * n
+    if incomplete == "fill":
+        return zip_longest(*args, fillvalue=fillvalue)
+    if incomplete == "strict":
+        return zip(*args, strict=True)
+    if incomplete == "ignore":
+        return zip(*args)
+    else:
+        raise ValueError("Expected fill, strict, or ignore")
+
+
+def get_phabricator(host: Optional[str], token: Optional[str]):
+    # uses information from ~/.arcrc if the token or host argument are None
+    phabricator = Phabricator(host=host, token=token)
+    phabricator.connect()
+    phabricator.update_interfaces()
+
+    return phabricator
+
+
+def load_mapping(mapping_filename):
+    ret = defaultdict(dict)
+
+    def push_mapping(item):
+        if not item:
+            return
+        item_type = item.pop("type")[1:].lower()
+
+        original_id = item.pop("original_id")
+
+        if original_id in ret[item_type]:
+            logger.warn("Duplicate mapping for %s %s: %s", item_type, original_id, item)
+
+        ret[item_type][original_id] = item or True
+
+    with open(mapping_filename, "r") as f:
+        current_item = {}
+        in_file = False
+        for line in f.readlines():
+            line = line.strip().rstrip(")")
+
+            if not line:
+                continue
+
+            if line.startswith("#S(FORGERIE-GITLAB::MAPPED-ITEM"):
+                in_file = False
+                push_mapping(current_item)
+                current_item = {}
+
+                continue
+
+            if line.startswith("#S(FORGERIE-GITLAB::MAPPED-FILE"):
+                in_file = True
+
+            if in_file:
+                continue
+
+            k, v = line.split(None, 1)
+            if v == "NIL":
+                continue
+
+            key = k[1:].lower().replace("-", "_")
+
+            if key in ("id", "iid", "project_id"):
+                v = int(v)
+            elif v[0] == v[-1] == '"':
+                v = v[1:-1]
+
+            current_item[key] = v
+        else:
+            # push the last item when the read ends
+            push_mapping(current_item)
+
+    return ret
+
+
+def get_gitlab(gitlab_instance):
+    gl = gitlab.Gitlab.from_config(gitlab_instance)
+    gl.auth()
+
+    return gl
+
+
+def mark_phabricator_task_as_migrated(phabricator, task, gitlab_url, new_owner, do_it):
+    transactions = []
+
+    # Set owner/assignee to `gitlab-migration`
+    transactions.append(
+        {
+            "type": "owner",
+            "value": new_owner,
+        }
+    )
+
+    # Add migration comment
+    transactions.append(
+        {
+            "type": "comment",
+            "value": f"[[ {gitlab_url} | This task has been migrated to GitLab. ]]",
+        }
+    )
+
+    # Set status to migrated
+    transactions.append(
+        {
+            "type": "status",
+            "value": "migrated",
+        }
+    )
+
+    if logger.isEnabledFor(logging.DEBUG):
+        for transaction in transactions:
+            logger.debug(
+                "For task %s: %s -> %s",
+                task["id"],
+                transaction["type"],
+                transaction["value"],
+            )
+
+    if do_it:
+        logger.info("Marking task T%s migrated to %s", task["id"], gitlab_url)
+        phabricator.maniphest.edit(
+            objectIdentifier=task["phid"], transactions=transactions
+        )
+
+
+@click.command()
+@click.option(
+    "--gitlab",
+    "-g",
+    "gitlab_instance",
+    help="Which GitLab instance to use, as configured in the python-gitlab config",
+)
+@click.option(
+    "--phabricator-token",
+    "phabricator_token",
+    help="Phabricator API token",
+)
+@click.option(
+    "--phabricator-host",
+    "phabricator_host",
+    help="Phabricator host",
+)
+@click.option(
+    "--do-it",
+    "do_it",
+    is_flag=True,
+    help="Actually perform the operations",
+)
+@click.argument("mapping_file")
+def cli(gitlab_instance, phabricator_token, phabricator_host, do_it, mapping_file):
+    phab = get_phabricator(host=phabricator_host, token=phabricator_token)
+    me = phab.user.whoami()
+    if me.userName != "gitlab-migration":
+        print("This script must be run as the gitlab-migration user!")
+        sys.exit(2)
+
+    gl = get_gitlab(gitlab_instance)
+
+    mapping = load_mapping(mapping_file)
+
+    maniphest_tasks = {}
+    for group in grouper(mapping["ticket-completed"], n=20):
+        task_ids = [int(tid) for tid in group if tid]
+        task_group = phab.maniphest.search(constraints={"ids": task_ids})
+        for task in task_group["data"]:
+            maniphest_tasks[task["id"]] = task
+
+    for task_id in mapping["ticket-completed"]:
+        phab_task_id = int(task_id)
+
+        phab_task_status = maniphest_tasks[phab_task_id]["fields"]["status"]["value"]
+
+        if phab_task_status == "migrated":
+            logger.debug("Already migrated Phabricator task %s, skipping", phab_task_id)
+            continue
+
+        mapped_task = mapping["ticket"].get(task_id)
+        if not mapped_task:
+            logger.warning("Missing mapping for completed ticket %s ?!", task_id)
+            continue
+        gl_project = gl.projects.get(mapped_task["project_id"])
+        gl_issue = gl_project.issues.get(mapped_task["iid"])
+
+        mark_phabricator_task_as_migrated(
+            phabricator=phab,
+            task=maniphest_tasks[phab_task_id],
+            gitlab_url=gl_issue.web_url,
+            new_owner=me.phid,
+            do_it=do_it,
+        )
+
+
+if __name__ == "__main__":
+    logging.basicConfig(
+        level=logging.INFO, format="%(asctime)s %(name)s:%(levelname)s %(message)s"
+    )
+    cli(auto_envvar_prefix="SWH")