diff --git a/js/background.js b/js/background.js
index 1561e70f824..ca2a59ffaa0 100644
--- a/js/background.js
+++ b/js/background.js
@@ -15,7 +15,7 @@
     'use strict';
 
     const { Errors, Message } = window.Signal.Types;
-    const { context: migrationsContext } = window.Signal.Migrations;
+    const { upgradeMessageSchema } = window.Signal.Migrations;
 
     // Implicitly used in `indexeddb-backbonejs-adapter`:
     // https://github.com/signalapp/Signal-Desktop/blob/4033a9f8137e62ed286170ed5d4941982b1d3a64/components/indexeddb-backbonejs-adapter/backbone-indexeddb.js#L569
@@ -574,8 +574,7 @@
         return event.confirm();
       }
 
-      const upgradedMessage =
-        await Message.upgradeSchema(data.message, migrationsContext);
+      const upgradedMessage = await upgradeMessageSchema(data.message);
       await ConversationController.getOrCreateAndWait(
         messageDescriptor.id,
         messageDescriptor.type
diff --git a/js/models/conversations.js b/js/models/conversations.js
index fc4dbd3b774..72ff8239460 100644
--- a/js/models/conversations.js
+++ b/js/models/conversations.js
@@ -10,7 +10,7 @@
    window.Whisper = window.Whisper || {};
 
    const { Attachment, Message } = window.Signal.Types;
-   const { context: migrationContext } = window.Signal.Migrations;
+   const { upgradeMessageSchema, loadAttachmentData } = window.Signal.Migrations;
 
    // TODO: Factor out private and group subclasses of Conversation
 
@@ -618,7 +618,7 @@
           now
         );
 
-        const messageWithSchema = await Message.upgradeSchema({
+        const messageWithSchema = await upgradeMessageSchema({
           type: 'outgoing',
           body,
           conversationId: this.id,
@@ -627,7 +627,7 @@
           received_at: now,
           expireTimer: this.get('expireTimer'),
           recipients: this.getRecipients(),
-        }, migrationContext);
+        });
         const message = this.messageCollection.add(messageWithSchema);
         if (this.isPrivate()) {
           message.set({ destination: this.id });
@@ -657,9 +657,8 @@
           profileKey = storage.get('profileKey');
         }
 
-        const loadData = Attachment.loadData(migrationContext.readAttachmentData);
         const attachmentsWithData =
-            await Promise.all(messageWithSchema.attachments.map(loadData));
+            await Promise.all(messageWithSchema.attachments.map(loadAttachmentData));
         message.send(sendFunction(
           this.get('id'),
           body,
diff --git a/js/models/messages.js b/js/models/messages.js
index fdbcc98e7d1..1022c14280f 100644
--- a/js/models/messages.js
+++ b/js/models/messages.js
@@ -5,7 +5,7 @@
     window.Whisper = window.Whisper || {};
 
     const { Attachment, Message: TypedMessage } = window.Signal.Types;
-    const { context: migrationContext } = window.Signal.Migrations;
+    const { deleteAttachmentData } = window.Signal.Migrations;
 
     var Message  = window.Whisper.Message = Backbone.Model.extend({
         database  : Whisper.Database,
@@ -147,9 +147,7 @@
         async onDestroy() {
           this.revokeImageUrl();
           const attachments = this.get('attachments');
-          const deleteData =
-            Attachment.deleteData(migrationContext.deleteAttachmentData);
-          await Promise.all(attachments.map(deleteData));
+          await Promise.all(attachments.map(deleteAttachmentData));
         },
         /* jshint ignore:end */
         /* eslint-disable */
diff --git a/js/views/message_view.js b/js/views/message_view.js
index fcde0c155c1..866cba27a8a 100644
--- a/js/views/message_view.js
+++ b/js/views/message_view.js
@@ -7,7 +7,7 @@
     window.Whisper = window.Whisper || {};
 
     const { Attachment } = window.Signal.Types;
-    const { context: migrationContext } = window.Signal.Migrations;
+    const { loadAttachmentData } = window.Signal.Migrations;
 
     var URL_REGEX = /(^|[\s\n]|<br\/?>)((?:https?|ftp):\/\/[\-A-Z0-9\u00A0-\uD7FF\uE000-\uFDCF\uFDF0-\uFFFD+\u0026\u2019@#\/%?=()~_|!:,.;]*[\-A-Z0-9+\u0026@#\/%=~()_|])/gi;
 
@@ -416,11 +416,10 @@
         return this.loadedAttachmentViews;
       }
 
-      const loadData = Attachment.loadData(migrationContext.readAttachmentData);
       const attachments = this.model.get('attachments') || [];
       const loadedAttachmentViews = Promise.all(attachments.map(attachment =>
         new Promise(async (resolve) => {
-          const attachmentWithData = await loadData(attachment);
+          const attachmentWithData = await loadAttachmentData(attachment);
           const view = new Whisper.AttachmentView({
             model: attachmentWithData,
             timestamp: this.model.get('sent_at'),
diff --git a/preload.js b/preload.js
index cc30a4b4e14..15185624259 100644
--- a/preload.js
+++ b/preload.js
@@ -4,7 +4,9 @@
   console.log('preload');
   const electron = require('electron');
 
+  const Attachment = require('./js/modules/types/attachment');
   const Attachments = require('./app/attachments');
+  const Message = require('./js/modules/types/message');
 
   const { app } = electron.remote;
 
@@ -113,25 +115,27 @@
   const readAttachmentData = Attachments.readData(attachmentsPath);
   const writeAttachmentData = Attachments.writeData(attachmentsPath);
 
+  // Injected context functions to keep `Message` agnostic from Electron:
+  const upgradeSchemaContext = {
+    writeAttachmentData,
+  };
+  const upgradeMessageSchema = message =>
+    Message.upgradeSchema(message, upgradeSchemaContext);
+
   window.Signal = window.Signal || {};
   window.Signal.Logs = require('./js/modules/logs');
   window.Signal.OS = require('./js/modules/os');
   window.Signal.Backup = require('./js/modules/backup');
   window.Signal.Crypto = require('./js/modules/crypto');
-
-  window.Signal.Migrations = window.Signal.Migrations || {};
-  // Injected context functions to keep `Message` agnostic from Electron:
-  window.Signal.Migrations.context = {
-    deleteAttachmentData,
-    readAttachmentData,
-    writeAttachmentData,
-  };
+  window.Signal.Migrations = {};
+  window.Signal.Migrations.loadAttachmentData = Attachment.loadData(readAttachmentData);
+  window.Signal.Migrations.deleteAttachmentData = Attachment.deleteData(deleteAttachmentData);
+  window.Signal.Migrations.upgradeMessageSchema = upgradeMessageSchema;
   window.Signal.Migrations.V17 = require('./js/modules/migrations/17');
-
   window.Signal.Types = window.Signal.Types || {};
-  window.Signal.Types.Attachment = require('./js/modules/types/attachment');
+  window.Signal.Types.Attachment = Attachment;
   window.Signal.Types.Errors = require('./js/modules/types/errors');
-  window.Signal.Types.Message = require('./js/modules/types/message');
+  window.Signal.Types.Message = Message;
   window.Signal.Types.MIME = require('./js/modules/types/mime');
   window.Signal.Types.Settings = require('./js/modules/types/settings');