diff --git a/js/background.js b/js/background.js
index b1a02af86bb9..65c5ef8bcdee 100644
--- a/js/background.js
+++ b/js/background.js
@@ -338,6 +338,7 @@
         db,
         clearStores: Whisper.Database.clearStores,
         handleDOMException: Whisper.Database.handleDOMException,
+        arrayBufferToString: textsecure.MessageReceiver.arrayBufferToString,
         countCallback: count => {
           window.log.info(`Migration: ${count} messages complete`);
           showMigrationStatus(count);
diff --git a/js/modules/migrate_to_sql.js b/js/modules/migrate_to_sql.js
index 36c8cb015da1..fff080d786c9 100644
--- a/js/modules/migrate_to_sql.js
+++ b/js/modules/migrate_to_sql.js
@@ -1,6 +1,6 @@
 /* global window, IDBKeyRange */
 
-const { includes, isFunction, isString, last } = require('lodash');
+const { includes, isFunction, isString, last, forEach } = require('lodash');
 const {
   saveMessages,
   _removeMessages,
@@ -25,6 +25,7 @@ async function migrateToSQL({
   clearStores,
   handleDOMException,
   countCallback,
+  arrayBufferToString,
 }) {
   if (!db) {
     throw new Error('Need db for IndexedDB connection!');
@@ -32,6 +33,9 @@ async function migrateToSQL({
   if (!isFunction(clearStores)) {
     throw new Error('Need clearStores function!');
   }
+  if (!isFunction(arrayBufferToString)) {
+    throw new Error('Need arrayBufferToString function!');
+  }
   if (!isFunction(handleDOMException)) {
     throw new Error('Need handleDOMException function!');
   }
@@ -78,7 +82,21 @@ async function migrateToSQL({
     // eslint-disable-next-line no-await-in-loop
     const status = await migrateStoreToSQLite({
       db,
-      save: saveUnprocesseds,
+      save: async array => {
+        forEach(array, item => {
+          // In the new database, we can't store ArrayBuffers, so we turn these two fields
+          //   into strings like MessageReceiver now does before save.
+          if (item.envelope) {
+            // eslint-disable-next-line no-param-reassign
+            item.envelope = arrayBufferToString(item.envelope);
+          }
+          if (item.decrypted) {
+            // eslint-disable-next-line no-param-reassign
+            item.decrypted = arrayBufferToString(item.decrypted);
+          }
+        });
+        await saveUnprocesseds(array);
+      },
       remove: removeUnprocessed,
       storeName: 'unprocessed',
       handleDOMException,
diff --git a/libtextsecure/message_receiver.js b/libtextsecure/message_receiver.js
index a68f794e363a..871b69e2e578 100644
--- a/libtextsecure/message_receiver.js
+++ b/libtextsecure/message_receiver.js
@@ -31,6 +31,11 @@ function MessageReceiver(username, password, signalingKey, options = {}) {
   }
 }
 
+MessageReceiver.stringToArrayBuffer = string =>
+  dcodeIO.ByteBuffer.wrap(string, 'binary').toArrayBuffer();
+MessageReceiver.arrayBufferToString = arrayBuffer =>
+  dcodeIO.ByteBuffer.wrap(arrayBuffer).toString('binary');
+
 MessageReceiver.prototype = new textsecure.EventTarget();
 MessageReceiver.prototype.extend({
   constructor: MessageReceiver,
@@ -269,10 +274,10 @@ MessageReceiver.prototype.extend({
     try {
       let envelopePlaintext = item.envelope;
 
-      // Up until 0.42.6 we stored envelope and decrypted as strings in IndexedDB,
-      //   so we need to be ready for them.
       if (typeof envelopePlaintext === 'string') {
-        envelopePlaintext = this.stringToArrayBuffer(envelopePlaintext);
+        envelopePlaintext = MessageReceiver.stringToArrayBuffer(
+          envelopePlaintext
+        );
       }
       const envelope = textsecure.protobuf.Envelope.decode(envelopePlaintext);
 
@@ -280,7 +285,9 @@ MessageReceiver.prototype.extend({
       if (decrypted) {
         let payloadPlaintext = decrypted;
         if (typeof payloadPlaintext === 'string') {
-          payloadPlaintext = this.stringToArrayBuffer(payloadPlaintext);
+          payloadPlaintext = MessageReceiver.stringToArrayBuffer(
+            payloadPlaintext
+          );
         }
         this.queueDecryptedEnvelope(envelope, payloadPlaintext);
       } else {
@@ -312,13 +319,6 @@ MessageReceiver.prototype.extend({
       envelope.sourceDevice
     } ${envelope.timestamp.toNumber()}`;
   },
-  stringToArrayBuffer(string) {
-    // eslint-disable-next-line new-cap
-    return dcodeIO.ByteBuffer.wrap(string, 'binary').toArrayBuffer();
-  },
-  arrayBufferToString(arrayBuffer) {
-    return dcodeIO.ByteBuffer.wrap(arrayBuffer).toString('binary');
-  },
   getAllFromCache() {
     window.log.info('getAllFromCache');
     return textsecure.storage.unprocessed.getAll().then(items => {
@@ -356,7 +356,7 @@ MessageReceiver.prototype.extend({
     const id = this.getEnvelopeId(envelope);
     const data = {
       id,
-      envelope: this.arrayBufferToString(plaintext),
+      envelope: MessageReceiver.arrayBufferToString(plaintext),
       timestamp: Date.now(),
       attempts: 1,
     };
@@ -365,7 +365,7 @@ MessageReceiver.prototype.extend({
   updateCache(envelope, plaintext) {
     const id = this.getEnvelopeId(envelope);
     const data = {
-      decrypted: this.arrayBufferToString(plaintext),
+      decrypted: MessageReceiver.arrayBufferToString(plaintext),
     };
     return textsecure.storage.unprocessed.update(id, data);
   },