diff --git a/src/com/android/providers/telephony/TelephonyBackupAgent.java b/src/com/android/providers/telephony/TelephonyBackupAgent.java
index b88cd6b..3d32bef 100644
--- a/src/com/android/providers/telephony/TelephonyBackupAgent.java
+++ b/src/com/android/providers/telephony/TelephonyBackupAgent.java
@@ -16,6 +16,7 @@
 
 package com.android.providers.telephony;
 
+import android.annotation.NonNull;
 import android.annotation.TargetApi;
 import android.app.AlarmManager;
 import android.app.IntentService;
@@ -443,48 +444,54 @@
             return;
         }
 
-        int messagesWritten = 0;
+        // Backups consist of multiple chunks; each chunk consists of a set of messages
+        // of the same type in a chronological order.
+        BackupChunkInformation chunk;
         try (JsonWriter jsonWriter = getJsonWriter(fileName)) {
             if (fileName.endsWith(SMS_BACKUP_FILE_SUFFIX)) {
-                messagesWritten = putSmsMessagesToJson(cursor, jsonWriter);
+                chunk = putSmsMessagesToJson(cursor, jsonWriter);
             } else {
-                messagesWritten = putMmsMessagesToJson(cursor, jsonWriter);
+                chunk = putMmsMessagesToJson(cursor, jsonWriter);
             }
         }
-        backupFile(messagesWritten, fileName, data);
+        backupFile(chunk, fileName, data);
     }
 
     @VisibleForTesting
-    int putMmsMessagesToJson(Cursor cursor,
+    @NonNull
+    BackupChunkInformation putMmsMessagesToJson(Cursor cursor,
                              JsonWriter jsonWriter) throws IOException {
+        BackupChunkInformation results = new BackupChunkInformation();
         jsonWriter.beginArray();
-        int msgCount;
-        for (msgCount = 0; msgCount < mMaxMsgPerFile && !cursor.isAfterLast();
+        for (; results.count < mMaxMsgPerFile && !cursor.isAfterLast();
                 cursor.moveToNext()) {
-            msgCount += writeMmsToWriter(jsonWriter, cursor);
+            writeMmsToWriter(jsonWriter, cursor, results);
         }
         jsonWriter.endArray();
-        return msgCount;
+        return results;
     }
 
     @VisibleForTesting
-    int putSmsMessagesToJson(Cursor cursor, JsonWriter jsonWriter) throws IOException {
-
+    @NonNull
+    BackupChunkInformation putSmsMessagesToJson(Cursor cursor, JsonWriter jsonWriter)
+      throws IOException {
+        BackupChunkInformation results = new BackupChunkInformation();
         jsonWriter.beginArray();
-        int msgCount;
-        for (msgCount = 0; msgCount < mMaxMsgPerFile && !cursor.isAfterLast();
-                ++msgCount, cursor.moveToNext()) {
-            writeSmsToWriter(jsonWriter, cursor);
+        for (; results.count < mMaxMsgPerFile && !cursor.isAfterLast();
+                ++results.count, cursor.moveToNext()) {
+            writeSmsToWriter(jsonWriter, cursor, results);
         }
         jsonWriter.endArray();
-        return msgCount;
+        return results;
     }
 
-    private void backupFile(int messagesWritten, String fileName, FullBackupDataOutput data)
+    private void backupFile(BackupChunkInformation chunkInformation, String fileName,
+        FullBackupDataOutput data)
             throws IOException {
         final File file = new File(getFilesDir().getPath() + "/" + fileName);
+        file.setLastModified(chunkInformation.timestamp);
         try {
-            if (messagesWritten > 0) {
+            if (chunkInformation.count > 0) {
                 if (mBytesOverQuota > 0) {
                     mBytesOverQuota -= file.length();
                     return;
@@ -703,7 +710,8 @@
                 subscriptionInfo.getCountryIso().toUpperCase(Locale.US));
     }
 
-    private void writeSmsToWriter(JsonWriter jsonWriter, Cursor cursor) throws IOException {
+    private void writeSmsToWriter(JsonWriter jsonWriter, Cursor cursor,
+            BackupChunkInformation chunk) throws IOException {
         jsonWriter.beginObject();
 
         for (int i=0; i<cursor.getColumnCount(); ++i) {
@@ -726,12 +734,31 @@
                     break;
                 case Telephony.Sms._ID:
                     break;
+                case Telephony.Sms.DATE:
+                case Telephony.Sms.DATE_SENT:
+                    chunk.timestamp = findNewestValue(chunk.timestamp, value);
+                    jsonWriter.name(name).value(value);
+                    break;
                 default:
                     jsonWriter.name(name).value(value);
                     break;
             }
         }
         jsonWriter.endObject();
+    }
+
+    private long findNewestValue(long current, String latest) {
+        if(latest == null) {
+            return current;
+        }
+
+        try {
+            long latestLong = Long.valueOf(latest);
+            return Math.max(current, latestLong);
+        } catch (NumberFormatException e) {
+            Log.d(TAG, "Unable to parse value "+latest);
+            return current;
+        }
 
     }
 
@@ -838,12 +865,13 @@
         return recipients;
     }
 
-    private int writeMmsToWriter(JsonWriter jsonWriter, Cursor cursor) throws IOException {
+    private void writeMmsToWriter(JsonWriter jsonWriter, Cursor cursor,
+            BackupChunkInformation chunk) throws IOException {
         final int mmsId = cursor.getInt(ID_IDX);
         final MmsBody body = getMmsBody(mmsId);
         // We backup any message that contains text, but only backup the text part.
         if (body == null || body.text == null) {
-            return 0;
+            return;
         }
 
         boolean subjectNull = true;
@@ -872,6 +900,11 @@
                 case Telephony.Mms._ID:
                 case Telephony.Mms.SUBJECT_CHARSET:
                     break;
+                case Telephony.Mms.DATE:
+                case Telephony.Mms.DATE_SENT:
+                    chunk.timestamp = findNewestValue(chunk.timestamp, value);
+                    jsonWriter.name(name).value(value);
+                    break;
                 case Telephony.Mms.SUBJECT:
                     subjectNull = false;
                 default:
@@ -891,7 +924,7 @@
             writeStringToWriter(jsonWriter, cursor, Telephony.Mms.SUBJECT_CHARSET);
         }
         jsonWriter.endObject();
-        return 1;
+        chunk.count++;
     }
 
     private Mms readMmsFromReader(JsonReader jsonReader) throws IOException {
@@ -1407,4 +1440,12 @@
     public static boolean getIsRestoring() {
         return sIsRestoring;
     }
+
+    private static class BackupChunkInformation {
+        // Timestamp of the recent message in the file
+        private long timestamp;
+
+        // The number of messages in the backup file
+        private int count = 0;
+    }
 }
diff --git a/tests/src/com/android/providers/telephony/TelephonyBackupAgentTest.java b/tests/src/com/android/providers/telephony/TelephonyBackupAgentTest.java
index 37cf6e3..b1cd5e4 100644
--- a/tests/src/com/android/providers/telephony/TelephonyBackupAgentTest.java
+++ b/tests/src/com/android/providers/telephony/TelephonyBackupAgentTest.java
@@ -16,7 +16,10 @@
 
 package com.android.providers.telephony;
 
+import static org.junit.Assert.assertArrayEquals;
+
 import android.annotation.TargetApi;
+import android.app.backup.BackupDataOutput;
 import android.app.backup.FullBackupDataOutput;
 import android.content.ContentProvider;
 import android.content.ContentResolver;
@@ -26,6 +29,7 @@
 import android.database.Cursor;
 import android.net.Uri;
 import android.os.Build;
+import android.os.ParcelFileDescriptor;
 import android.provider.BaseColumns;
 import android.provider.Telephony;
 import android.test.AndroidTestCase;
@@ -40,22 +44,29 @@
 import android.util.Log;
 import android.util.SparseArray;
 
+import libcore.io.IoUtils;
+
 import com.google.android.mms.pdu.CharacterSets;
 
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
 
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
 import java.io.StringReader;
 import java.io.StringWriter;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.TimeUnit;
 
 /**
  * Tests for testing backup/restore of SMS and text MMS messages.
@@ -684,6 +695,44 @@
         assertEquals(backupSizeAfterSecondQuotaHit, fullBackupDataOutput.getSize());
     }
 
+    /**
+     * Test backups are consistent between runs. This ensures that when no data
+     * has changed between backup runs we don't generate a diff which needs to
+     * be sent to the server.
+     * @throws Exception
+     */
+    public void testBackup_WithoutChanges_DoesNotChangeOutput() throws Exception {
+        mSmsTable.addAll(Arrays.asList(mSmsRows));
+        mMmsTable.addAll(Arrays.asList(mMmsRows));
+
+        byte[] firstBackup = getBackup("1");
+        // Ensure there is some time between backup runs. This is the way to identify
+        // time dependent backup contents.
+        Thread.sleep(TimeUnit.MILLISECONDS.convert(1, TimeUnit.SECONDS));
+        byte[] secondBackup = getBackup("2");
+
+        // Make sure something has been backed up.
+        assertFalse(firstBackup == null || firstBackup.length == 0);
+
+        // Make sure the two backups are the same.
+        assertArrayEquals(firstBackup, secondBackup);
+    }
+
+    private byte[] getBackup(String runId) throws IOException {
+        File cacheDir = getContext().getCacheDir();
+        File backupOutput = File.createTempFile("backup", runId, cacheDir);
+        ParcelFileDescriptor outputFd =
+                ParcelFileDescriptor.open(backupOutput, ParcelFileDescriptor.MODE_WRITE_ONLY);
+        try {
+            FullBackupDataOutput fullBackupDataOutput = new FullBackupDataOutput(outputFd);
+            mTelephonyBackupAgent.onFullBackup(fullBackupDataOutput);
+            return IoUtils.readFileAsByteArray(backupOutput.getAbsolutePath());
+        } finally {
+            outputFd.close();
+            backupOutput.delete();
+        }
+    }
+
     // Adding random keys to JSON to test handling it by the BackupAgent on restore.
     private String addRandomDataToJson(String jsonString) throws JSONException {
         JSONArray jsonArray = new JSONArray(jsonString);