diff --git a/services/core/java/com/android/server/AppStateTracker.java b/services/core/java/com/android/server/AppStateTracker.java
index 3a7b5d6835077..207e007cc62fd 100644
--- a/services/core/java/com/android/server/AppStateTracker.java
+++ b/services/core/java/com/android/server/AppStateTracker.java
@@ -700,14 +700,16 @@ public class AppStateTracker {
                 Slog.d(TAG,"onAppIdleStateChanged: " + packageName + " u" + userId
                         + (idle ? " idle" : " active") + " " + bucket);
             }
-            final boolean changed;
-            if (bucket == UsageStatsManager.STANDBY_BUCKET_EXEMPTED) {
-                changed = mExemptedPackages.add(userId, packageName);
-            } else {
-                changed = mExemptedPackages.remove(userId, packageName);
-            }
-            if (changed) {
-                mHandler.notifyExemptChanged();
+            synchronized (mLock) {
+                final boolean changed;
+                if (bucket == UsageStatsManager.STANDBY_BUCKET_EXEMPTED) {
+                    changed = mExemptedPackages.add(userId, packageName);
+                } else {
+                    changed = mExemptedPackages.remove(userId, packageName);
+                }
+                if (changed) {
+                    mHandler.notifyExemptChanged();
+                }
             }
         }