diff --git a/js/libtextsecure.js b/js/libtextsecure.js
index 05911bff1..bb4731445 100644
--- a/js/libtextsecure.js
+++ b/js/libtextsecure.js
@@ -37510,7 +37510,10 @@ window.axolotl.protocol = function(storage_interface) {
     }
 
     // return Promise(encoded [PreKey]WhisperMessage)
-    self.encryptMessageFor = function(deviceObject, pushMessageContent) {
+    self.encryptMessageFor = function(deviceObject, plaintext) {
+        if (!(plaintext instanceof ArrayBuffer)) {
+            throw new Error("Expected plaintext to be an ArrayBuffer");
+        }
         return storage_interface.getMyIdentityKey().then(function(ourIdentityKey) {
             return storage_interface.getMyRegistrationId().then(function(myRegistrationId) {
                 return crypto_storage.getOpenSession(deviceObject.encodedNumber).then(function(session) {
@@ -37518,7 +37521,6 @@ window.axolotl.protocol = function(storage_interface) {
 
                     var doEncryptPushMessageContent = function() {
                         var msg = new axolotlInternal.protobuf.WhisperMessage();
-                        var plaintext = axolotlInternal.utils.convertToArrayBuffer(pushMessageContent.encode());
 
                         var paddedPlaintext = new Uint8Array(getPaddedMessageLength(plaintext.byteLength));
                         paddedPlaintext.set(new Uint8Array(plaintext));
@@ -39864,6 +39866,7 @@ MessageSender.prototype = {
     // message == DataMessage or ContentMessage proto
     encryptToDevices: function(timestamp, number, deviceObjectList, message) {
         var legacy = (message instanceof textsecure.protobuf.DataMessage);
+        var plaintext = message.toArrayBuffer();
         var relay = deviceObjectList[0].relay;
         for (var i=1; i < deviceObjectList.length; ++i) {
             if (deviceObjectList[i].relay !== relay) {
@@ -39871,7 +39874,7 @@ MessageSender.prototype = {
             }
         }
         return Promise.all(deviceObjectList.map(function(device) {
-            return textsecure.protocol_wrapper.encryptMessageFor(device, message).then(function(encryptedMsg) {
+            return textsecure.protocol_wrapper.encryptMessageFor(device, plaintext).then(function(encryptedMsg) {
                 return textsecure.protocol_wrapper.getRegistrationId(device.encodedNumber).then(function(registrationId) {
                     return textsecure.storage.devices.removeTempKeysFromDevice(device.encodedNumber).then(function() {
                         var json = {
diff --git a/libtextsecure/libaxolotl.js b/libtextsecure/libaxolotl.js
index 2f15bb0b4..63094080b 100644
--- a/libtextsecure/libaxolotl.js
+++ b/libtextsecure/libaxolotl.js
@@ -37412,7 +37412,10 @@ window.axolotl.protocol = function(storage_interface) {
     }
 
     // return Promise(encoded [PreKey]WhisperMessage)
-    self.encryptMessageFor = function(deviceObject, pushMessageContent) {
+    self.encryptMessageFor = function(deviceObject, plaintext) {
+        if (!(plaintext instanceof ArrayBuffer)) {
+            throw new Error("Expected plaintext to be an ArrayBuffer");
+        }
         return storage_interface.getMyIdentityKey().then(function(ourIdentityKey) {
             return storage_interface.getMyRegistrationId().then(function(myRegistrationId) {
                 return crypto_storage.getOpenSession(deviceObject.encodedNumber).then(function(session) {
@@ -37420,7 +37423,6 @@ window.axolotl.protocol = function(storage_interface) {
 
                     var doEncryptPushMessageContent = function() {
                         var msg = new axolotlInternal.protobuf.WhisperMessage();
-                        var plaintext = axolotlInternal.utils.convertToArrayBuffer(pushMessageContent.encode());
 
                         var paddedPlaintext = new Uint8Array(getPaddedMessageLength(plaintext.byteLength));
                         paddedPlaintext.set(new Uint8Array(plaintext));
diff --git a/libtextsecure/sendmessage.js b/libtextsecure/sendmessage.js
index 088b8052e..528e15262 100644
--- a/libtextsecure/sendmessage.js
+++ b/libtextsecure/sendmessage.js
@@ -11,6 +11,7 @@ MessageSender.prototype = {
     // message == DataMessage or ContentMessage proto
     encryptToDevices: function(timestamp, number, deviceObjectList, message) {
         var legacy = (message instanceof textsecure.protobuf.DataMessage);
+        var plaintext = message.toArrayBuffer();
         var relay = deviceObjectList[0].relay;
         for (var i=1; i < deviceObjectList.length; ++i) {
             if (deviceObjectList[i].relay !== relay) {
@@ -18,7 +19,7 @@ MessageSender.prototype = {
             }
         }
         return Promise.all(deviceObjectList.map(function(device) {
-            return textsecure.protocol_wrapper.encryptMessageFor(device, message).then(function(encryptedMsg) {
+            return textsecure.protocol_wrapper.encryptMessageFor(device, plaintext).then(function(encryptedMsg) {
                 return textsecure.protocol_wrapper.getRegistrationId(device.encodedNumber).then(function(registrationId) {
                     return textsecure.storage.devices.removeTempKeysFromDevice(device.encodedNumber).then(function() {
                         var json = {