diff --git a/core/java/android/app/NotificationHistory.java b/core/java/android/app/NotificationHistory.java
index 8ba39a883555a..909a476f3c941 100644
--- a/core/java/android/app/NotificationHistory.java
+++ b/core/java/android/app/NotificationHistory.java
@@ -24,6 +24,8 @@ import android.os.Parcelable;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
@@ -311,11 +313,23 @@ public final class NotificationHistory implements Parcelable {
         mHistoryCount++;
     }
 
+    /**
+     * Used when populating a history from disk; adds an historical notification.
+     */
+    public void addNewNotificationToWrite(@NonNull HistoricalNotification notification) {
+        if (notification == null) {
+            return;
+        }
+        mNotificationsToWrite.add(0, notification);
+        mHistoryCount++;
+    }
+
     public void addNotificationsToWrite(@NonNull NotificationHistory notificationHistory) {
         for (HistoricalNotification hn : notificationHistory.getNotificationsToWrite()) {
-            // TODO: consider merging by date
             addNotificationToWrite(hn);
         }
+        Collections.sort(mNotificationsToWrite,
+                (o1, o2) -> -1 * Long.compare(o1.getPostedTimeMs(), o2.getPostedTimeMs()));
         poolStringsFromNotifications();
     }
 
diff --git a/core/tests/coretests/src/android/app/NotificationHistoryTest.java b/core/tests/coretests/src/android/app/NotificationHistoryTest.java
index f9a6a5c2af4d7..0a21875fd77de 100644
--- a/core/tests/coretests/src/android/app/NotificationHistoryTest.java
+++ b/core/tests/coretests/src/android/app/NotificationHistoryTest.java
@@ -116,25 +116,28 @@ public class NotificationHistoryTest {
     @Test
     public void testAddNotificationsToWrite() {
         NotificationHistory history = new NotificationHistory();
-        HistoricalNotification n = getHistoricalNotification(0);
+        HistoricalNotification n = getHistoricalNotification(3);
         HistoricalNotification n2 = getHistoricalNotification(1);
+        HistoricalNotification n5 = getHistoricalNotification(0);
         history.addNotificationToWrite(n2);
         history.addNotificationToWrite(n);
+        history.addNotificationToWrite(n5);
 
         NotificationHistory secondHistory = new NotificationHistory();
-        HistoricalNotification n3 = getHistoricalNotification(2);
-        HistoricalNotification n4 = getHistoricalNotification(3);
+        HistoricalNotification n3 = getHistoricalNotification(4);
+        HistoricalNotification n4 = getHistoricalNotification(2);
         secondHistory.addNotificationToWrite(n4);
         secondHistory.addNotificationToWrite(n3);
 
         history.addNotificationsToWrite(secondHistory);
 
-        assertThat(history.getNotificationsToWrite().size()).isEqualTo(4);
-        assertThat(history.getNotificationsToWrite().get(0)).isSameAs(n2);
+        assertThat(history.getNotificationsToWrite().size()).isEqualTo(5);
+        assertThat(history.getNotificationsToWrite().get(0)).isSameAs(n3);
         assertThat(history.getNotificationsToWrite().get(1)).isSameAs(n);
         assertThat(history.getNotificationsToWrite().get(2)).isSameAs(n4);
-        assertThat(history.getNotificationsToWrite().get(3)).isSameAs(n3);
-        assertThat(history.getHistoryCount()).isEqualTo(4);
+        assertThat(history.getNotificationsToWrite().get(3)).isSameAs(n2);
+        assertThat(history.getNotificationsToWrite().get(4)).isSameAs(n5);
+        assertThat(history.getHistoryCount()).isEqualTo(5);
 
         assertThat(history.getPooledStringsToWrite()).asList().contains(n2.getChannelName());
         assertThat(history.getPooledStringsToWrite()).asList().contains(n4.getPackage());
diff --git a/services/core/java/com/android/server/notification/NotificationHistoryDatabase.java b/services/core/java/com/android/server/notification/NotificationHistoryDatabase.java
index e1ebdf17ef7c0..e8cb1632bdc32 100644
--- a/services/core/java/com/android/server/notification/NotificationHistoryDatabase.java
+++ b/services/core/java/com/android/server/notification/NotificationHistoryDatabase.java
@@ -172,7 +172,7 @@ public class NotificationHistoryDatabase {
 
     public void addNotification(final HistoricalNotification notification) {
         synchronized (mLock) {
-            mBuffer.addNotificationToWrite(notification);
+            mBuffer.addNewNotificationToWrite(notification);
             // Each time we have new history to write to disk, schedule a write in [interval] ms
             if (mBuffer.getHistoryCount() == 1) {
                 mFileWriteHandler.postDelayed(mWriteBufferRunnable, WRITE_BUFFER_INTERVAL_MS);
diff --git a/services/tests/uiservicestests/src/com/android/server/notification/NotificationHistoryDatabaseTest.java b/services/tests/uiservicestests/src/com/android/server/notification/NotificationHistoryDatabaseTest.java
index 9ad6986f2f90e..5b5ad877081cf 100644
--- a/services/tests/uiservicestests/src/com/android/server/notification/NotificationHistoryDatabaseTest.java
+++ b/services/tests/uiservicestests/src/com/android/server/notification/NotificationHistoryDatabaseTest.java
@@ -185,6 +185,20 @@ public class NotificationHistoryDatabaseTest extends UiServiceTestCase {
         verify(mFileWriteHandler, times(1)).postDelayed(any(), anyLong());
     }
 
+    @Test
+    public void testAddNotification_newestFirst() {
+        HistoricalNotification n = getHistoricalNotification(1);
+        HistoricalNotification n2 = getHistoricalNotification(2);
+
+        mDataBase.addNotification(n);
+
+        // second add should not trigger another write
+        mDataBase.addNotification(n2);
+
+        assertThat(mDataBase.mBuffer.getNotificationsToWrite().get(0)).isEqualTo(n2);
+        assertThat(mDataBase.mBuffer.getNotificationsToWrite().get(1)).isEqualTo(n);
+    }
+
     @Test
     public void testReadNotificationHistory_readsAllFiles() throws Exception {
         for (long i = 10; i >= 5; i--) {