diff --git a/services/core/java/com/android/server/notification/NotificationUsageStats.java b/services/core/java/com/android/server/notification/NotificationUsageStats.java
index 00d7a7b9e0cb5..7b573da482e3e 100644
--- a/services/core/java/com/android/server/notification/NotificationUsageStats.java
+++ b/services/core/java/com/android/server/notification/NotificationUsageStats.java
@@ -384,7 +384,7 @@ public class NotificationUsageStats {
             noisyImportance = new ImportanceHistogram(context, "note_imp_noisy_");
             quietImportance = new ImportanceHistogram(context, "note_imp_quiet_");
             finalImportance = new ImportanceHistogram(context, "note_importance_");
-            enqueueRate = new RateEstimator(mCreated);
+            enqueueRate = new RateEstimator();
         }
 
         public AggregatedStats getPrevious() {
diff --git a/services/core/java/com/android/server/notification/RateEstimator.java b/services/core/java/com/android/server/notification/RateEstimator.java
index 4dc30a4c98bdd..c17db4acf3cd7 100644
--- a/services/core/java/com/android/server/notification/RateEstimator.java
+++ b/services/core/java/com/android/server/notification/RateEstimator.java
@@ -25,30 +25,43 @@ package com.android.server.notification;
 public class RateEstimator {
     private static final double RATE_ALPHA = 0.8;
     private static final double MINIMUM_DT = 0.0005;
-    private long mLastEventTime;
-    private float mInterarrivalTime;
+    private Long mLastEventTime;
+    private Float mInterarrivalTime;
 
-    public RateEstimator(long now) {
-        mLastEventTime = now;
-    }
+    public RateEstimator() {}
 
-    /** Update the estimate to account for an event that jsut happened. */
+    /** Update the estimate to account for an event that just happened. */
     public float update(long now) {
-        mInterarrivalTime = (float) getInterarrivalEstimate(now);
+        float rate;
+        if (mLastEventTime == null) {
+            // No last event time, rate is zero.
+            rate = 0f;
+        } else {
+            // Calculate the new inter-arrival time based on last event time.
+            mInterarrivalTime = (float) getInterarrivalEstimate(now);
+            rate = (float) (1.0 / mInterarrivalTime);
+        }
         mLastEventTime = now;
-        return (float) (1.0 / mInterarrivalTime);
+        return rate;
     }
 
     /** @return the estimated rate if there were a new event right now. */
     public float getRate(long now) {
+        if (mLastEventTime == null) {
+            return 0f;
+        }
         return (float) (1.0 / getInterarrivalEstimate(now));
     }
 
     /** @return the average inter-arrival time if there were a new event right now. */
     private double getInterarrivalEstimate(long now) {
-        // a*iat_old + (1-a)*(t_now-t_last)
         double dt = ((double) (now - mLastEventTime)) / 1000.0;
         dt = Math.max(dt, MINIMUM_DT);
+        if (mInterarrivalTime == null) {
+            // No last inter-arrival time, return the new value directly.
+            return dt;
+        }
+        // a*iat_old + (1-a)*(t_now-t_last)
         return (RATE_ALPHA * mInterarrivalTime + (1.0 - RATE_ALPHA) * dt);
     }
 }
diff --git a/services/tests/servicestests/src/com/android/server/notification/RateEstimatorTest.java b/services/tests/servicestests/src/com/android/server/notification/RateEstimatorTest.java
index cc0920f506a8a..b5698d5bd40bb 100644
--- a/services/tests/servicestests/src/com/android/server/notification/RateEstimatorTest.java
+++ b/services/tests/servicestests/src/com/android/server/notification/RateEstimatorTest.java
@@ -26,18 +26,18 @@ public class RateEstimatorTest extends AndroidTestCase {
     @Override
     public void setUp() {
         mTestStartTime = 1225731600000L;
-        mEstimator = new RateEstimator(mTestStartTime);
+        mEstimator = new RateEstimator();
     }
 
     @SmallTest
     public void testRunningTimeBackwardDoesntExplodeUpdate() throws Exception {
-        final float rate = mEstimator.update(mTestStartTime - 1000L);
-        assertFalse(Float.isInfinite(rate));
-        assertFalse(Float.isNaN(rate));
+        assertUpdateTime(mTestStartTime);
+        assertUpdateTime(mTestStartTime - 1000L);
     }
 
     @SmallTest
     public void testRunningTimeBackwardDoesntExplodeGet() throws Exception {
+        assertUpdateTime(mTestStartTime);
         final float rate = mEstimator.getRate(mTestStartTime - 1000L);
         assertFalse(Float.isInfinite(rate));
         assertFalse(Float.isNaN(rate));
@@ -45,13 +45,14 @@ public class RateEstimatorTest extends AndroidTestCase {
 
     @SmallTest
     public void testInstantaneousEventsDontExplodeUpdate() throws Exception {
-        final float rate = mEstimator.update(mTestStartTime);
-        assertFalse(Float.isInfinite(rate));
-        assertFalse(Float.isNaN(rate));
+        assertUpdateTime(mTestStartTime);
+        assertUpdateTime(mTestStartTime);
     }
 
     @SmallTest
     public void testInstantaneousEventsDontExplodeGet() throws Exception {
+        assertUpdateTime(mTestStartTime);
+        assertUpdateTime(mTestStartTime);
         final float rate = mEstimator.getRate(mTestStartTime);
         assertFalse(Float.isInfinite(rate));
         assertFalse(Float.isNaN(rate));
@@ -59,6 +60,7 @@ public class RateEstimatorTest extends AndroidTestCase {
 
     @SmallTest
     public void testCompactBurstIsEstimatedUnderTwoPercent() throws Exception {
+        assertUpdateTime(mTestStartTime);
         long eventStart = mTestStartTime + 1000; // start event a long time after initialization
         long nextEventTime = postEvents(eventStart, 1, 5); // five events at 1000Hz
         final float rate = mEstimator.getRate(nextEventTime);
@@ -67,6 +69,7 @@ public class RateEstimatorTest extends AndroidTestCase {
 
     @SmallTest
     public void testSustained1000HzBurstIsEstimatedOverNinetyPercent() throws Exception {
+        assertUpdateTime(mTestStartTime);
         long eventStart = mTestStartTime + 1000; // start event a long time after initialization
         long nextEventTime = postEvents(eventStart, 1, 100); // one hundred events at 1000Hz
         final float rate = mEstimator.getRate(nextEventTime);
@@ -75,6 +78,7 @@ public class RateEstimatorTest extends AndroidTestCase {
 
     @SmallTest
     public void testSustained100HzBurstIsEstimatedOverNinetyPercent() throws Exception {
+        assertUpdateTime(mTestStartTime);
         long eventStart = mTestStartTime + 1000; // start event a long time after initialization
         long nextEventTime = postEvents(eventStart, 10, 100); // one hundred events at 100Hz
         final float rate = mEstimator.getRate(nextEventTime);
@@ -84,6 +88,7 @@ public class RateEstimatorTest extends AndroidTestCase {
 
     @SmallTest
     public void testRecoverQuicklyAfterSustainedBurst() throws Exception {
+        assertUpdateTime(mTestStartTime);
         long eventStart = mTestStartTime + 1000; // start event a long time after initialization
         long nextEventTime = postEvents(eventStart, 10, 1000); // one hundred events at 100Hz
         final float rate = mEstimator.getRate(nextEventTime + 5000L); // two seconds later
@@ -92,12 +97,19 @@ public class RateEstimatorTest extends AndroidTestCase {
 
     @SmallTest
     public void testEstimateShouldNotOvershoot() throws Exception {
+        assertUpdateTime(mTestStartTime);
         long eventStart = mTestStartTime + 1000; // start event a long time after initialization
         long nextEventTime = postEvents(eventStart, 1, 1000); // one thousand events at 1000Hz
         final float rate = mEstimator.getRate(nextEventTime);
         assertLessThan("Rate", rate, 1000f);
     }
 
+    @SmallTest
+    public void testGetRateWithoutUpdate() throws Exception {
+        final float rate = mEstimator.getRate(mTestStartTime);
+        assertLessThan("Rate", rate, 0.1f);
+    }
+
     private void assertLessThan(String label, float a, float b)  {
         assertTrue(String.format("%s was %f, but should be less than %f", label, a, b), a < b);
     }
@@ -115,4 +127,10 @@ public class RateEstimatorTest extends AndroidTestCase {
         }
         return time;
     }
+
+    private void assertUpdateTime(long time) {
+        final float rate = mEstimator.update(time);
+        assertFalse(Float.isInfinite(rate));
+        assertFalse(Float.isNaN(rate));
+    }
 }