diff --git a/gnss/2.0/default/GnssMeasurement.h b/gnss/2.0/default/GnssMeasurement.h
index d8ffd59..151456c 100644
--- a/gnss/2.0/default/GnssMeasurement.h
+++ b/gnss/2.0/default/GnssMeasurement.h
@@ -61,10 +61,12 @@
     void stop();
     void reportMeasurement(const GnssData&);
 
+    // Guarded by mMutex
     static sp<IGnssMeasurementCallback> sCallback;
     std::atomic<long> mMinIntervalMillis;
     std::atomic<bool> mIsActive;
     std::thread mThread;
+    // Synchronization lock for sCallback
     mutable std::mutex mMutex;
 };