diff --git a/gnss/2.1/default/GnssAntennaInfo.h b/gnss/2.1/default/GnssAntennaInfo.h
index f4bfd24..c512e4e 100644
--- a/gnss/2.1/default/GnssAntennaInfo.h
+++ b/gnss/2.1/default/GnssAntennaInfo.h
@@ -47,10 +47,12 @@
     void reportAntennaInfo(
             const hidl_vec<IGnssAntennaInfoCallback::GnssAntennaInfo>& antennaInfo) const;
 
+    // Guarded by mMutex
     static sp<IGnssAntennaInfoCallback> sCallback;
     std::atomic<long> mMinIntervalMillis;
     std::atomic<bool> mIsActive;
     std::thread mThread;
+    // Synchronization lock for sCallback
     mutable std::mutex mMutex;
 };