diff --git a/updater_sample/Android.mk b/updater_sample/Android.mk
index 056ad66..7662111 100644
--- a/updater_sample/Android.mk
+++ b/updater_sample/Android.mk
@@ -18,8 +18,8 @@
 include $(CLEAR_VARS)
 
 LOCAL_PACKAGE_NAME := SystemUpdaterSample
-LOCAL_SDK_VERSION := system_current
 LOCAL_MODULE_TAGS := samples
+LOCAL_SDK_VERSION := system_current
 
 # TODO: enable proguard and use proguard.flags file
 LOCAL_PROGUARD_ENABLED := disabled
diff --git a/updater_sample/src/com/example/android/systemupdatersample/UpdateManager.java b/updater_sample/src/com/example/android/systemupdatersample/UpdateManager.java
index f5c2ea5..145cc83 100644
--- a/updater_sample/src/com/example/android/systemupdatersample/UpdateManager.java
+++ b/updater_sample/src/com/example/android/systemupdatersample/UpdateManager.java
@@ -39,6 +39,8 @@
 import java.util.function.DoubleConsumer;
 import java.util.function.IntConsumer;
 
+import javax.annotation.concurrent.GuardedBy;
+
 /**
  * Manages the update flow. It has its own state (in memory), separate from
  * {@link UpdateEngine}'s state. Asynchronously interacts with the {@link UpdateEngine}.
@@ -62,11 +64,16 @@
 
     private AtomicBoolean mManualSwitchSlotRequired = new AtomicBoolean(true);
 
+    @GuardedBy("mLock")
     private UpdateData mLastUpdateData = null;
 
+    @GuardedBy("mLock")
     private IntConsumer mOnStateChangeCallback = null;
+    @GuardedBy("mLock")
     private IntConsumer mOnEngineStatusUpdateCallback = null;
+    @GuardedBy("mLock")
     private DoubleConsumer mOnProgressUpdateCallback = null;
+    @GuardedBy("mLock")
     private IntConsumer mOnEngineCompleteCallback = null;
 
     private final Object mLock = new Object();