diff --git a/js/modules/signal.js b/js/modules/signal.js
index 5939c54c4..47450703b 100644
--- a/js/modules/signal.js
+++ b/js/modules/signal.js
@@ -129,9 +129,6 @@ const { QualifiedAddress } = require('../../ts/types/QualifiedAddress');
 // Views
 const Initialization = require('./views/initialization');
 
-// Workflow
-const MessageDataMigrator = require('./messages_data_migrator');
-
 // Processes / Services
 const {
   initializeGroupCredentialFetcher,
@@ -412,10 +409,6 @@ exports.setup = (options = {}) => {
     Initialization,
   };
 
-  const Workflow = {
-    MessageDataMigrator,
-  };
-
   return {
     Backbone,
     Components,
@@ -436,6 +429,5 @@ exports.setup = (options = {}) => {
     Types,
     Util,
     Views,
-    Workflow,
   };
 };
diff --git a/ts/background.ts b/ts/background.ts
index 5879097c3..87bfd698d 100644
--- a/ts/background.ts
+++ b/ts/background.ts
@@ -50,6 +50,7 @@ import { isMoreRecentThan, isOlderThan, toDayMillis } from './util/timestamp';
 import { isValidReactionEmoji } from './reactions/isValidReactionEmoji';
 import type { ConversationModel } from './models/conversations';
 import { getContact } from './messages/helpers';
+import { migrateMessageData } from './messages/migrateMessageData';
 import { createBatcher } from './util/batcher';
 import { updateConversationsWithUuidLookup } from './updateConversationsWithUuidLookup';
 import { initializeAllJobQueues } from './jobs/initializeAllJobQueues';
@@ -493,7 +494,6 @@ export async function startApp(): Promise<void> {
   //   of preload.js processing
   window.setImmediate = window.nodeSetImmediate;
 
-  const { MessageDataMigrator } = window.Signal.Workflow;
   const { removeDatabase: removeIndexedDB, doesDatabaseExist } =
     window.Signal.IndexedDB;
   const { Message } = window.Signal.Types;
@@ -827,8 +827,7 @@ export async function startApp(): Promise<void> {
       const NUM_MESSAGES_PER_BATCH = 1;
 
       if (!isMigrationWithIndexComplete) {
-        const batchWithIndex = await MessageDataMigrator.processNext({
-          BackboneMessageCollection: window.Whisper.MessageCollection,
+        const batchWithIndex = await migrateMessageData({
           numMessagesPerBatch: NUM_MESSAGES_PER_BATCH,
           upgradeMessageSchema,
           getMessagesNeedingUpgrade:
diff --git a/js/modules/messages_data_migrator.js b/ts/messages/migrateMessageData.ts
similarity index 60%
rename from js/modules/messages_data_migrator.js
rename to ts/messages/migrateMessageData.ts
index c63336887..51e9c81e4 100644
--- a/js/modules/messages_data_migrator.js
+++ b/ts/messages/migrateMessageData.ts
@@ -1,29 +1,49 @@
-// Copyright 2018-2020 Signal Messenger, LLC
+// Copyright 2018-2022 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-// Ensures that messages in database are at the right schema.
+import { isFunction, isNumber } from 'lodash';
+import * as Message from '../../js/modules/types/message';
+import type { MessageAttributesType } from '../model-types.d';
+import type { UUIDStringType } from '../types/UUID';
 
-/* global window */
-
-const { isFunction, isNumber } = require('lodash');
-
-const Message = require('./types/message');
-
-exports.processNext = async ({
-  BackboneMessageCollection,
+/**
+ * Ensures that messages in database are at the right schema.
+ */
+export async function migrateMessageData({
   numMessagesPerBatch,
   upgradeMessageSchema,
   getMessagesNeedingUpgrade,
   saveMessage,
   maxVersion = Message.CURRENT_SCHEMA_VERSION,
-} = {}) => {
-  if (!isFunction(BackboneMessageCollection)) {
-    throw new TypeError(
-      "'BackboneMessageCollection' (Whisper.MessageCollection)" +
-        ' constructor is required'
-    );
-  }
-
+}: Readonly<{
+  numMessagesPerBatch: number;
+  upgradeMessageSchema: (
+    message: MessageAttributesType,
+    options: { maxVersion: number }
+  ) => Promise<MessageAttributesType>;
+  getMessagesNeedingUpgrade: (
+    limit: number,
+    options: { maxVersion: number }
+  ) => Promise<Array<MessageAttributesType>>;
+  saveMessage: (
+    data: MessageAttributesType,
+    options: { ourUuid: UUIDStringType }
+  ) => Promise<string>;
+  maxVersion?: number;
+}>): Promise<
+  | {
+      done: true;
+      numProcessed: 0;
+    }
+  | {
+      done: boolean;
+      numProcessed: number;
+      fetchDuration: number;
+      upgradeDuration: number;
+      saveDuration: number;
+      totalDuration: number;
+    }
+> {
   if (!isNumber(numMessagesPerBatch)) {
     throw new TypeError("'numMessagesPerBatch' is required");
   }
@@ -39,10 +59,7 @@ exports.processNext = async ({
   try {
     messagesRequiringSchemaUpgrade = await getMessagesNeedingUpgrade(
       numMessagesPerBatch,
-      {
-        maxVersion,
-        MessageCollection: BackboneMessageCollection,
-      }
+      { maxVersion }
     );
   } catch (error) {
     window.SignalContext.log.error(
@@ -85,4 +102,4 @@ exports.processNext = async ({
     saveDuration,
     totalDuration,
   };
-};
+}
diff --git a/ts/window.d.ts b/ts/window.d.ts
index befef2992..7cb3f96a3 100644
--- a/ts/window.d.ts
+++ b/ts/window.d.ts
@@ -401,9 +401,6 @@ declare global {
         WhatsNewLink: typeof WhatsNewLink;
       };
       OS: typeof OS;
-      Workflow: {
-        MessageDataMigrator: WhatIsThis;
-      };
       IndexedDB: {
         removeDatabase: WhatIsThis;
         doesDatabaseExist: WhatIsThis;