diff --git a/gnss/2.0/default/GnssMeasurement.cpp b/gnss/2.0/default/GnssMeasurement.cpp
index d778d50..a3ea807 100644
--- a/gnss/2.0/default/GnssMeasurement.cpp
+++ b/gnss/2.0/default/GnssMeasurement.cpp
@@ -49,8 +49,8 @@
 
 Return<void> GnssMeasurement::close() {
     ALOGD("close");
-    std::unique_lock<std::mutex> lock(mMutex);
     stop();
+    std::unique_lock<std::mutex> lock(mMutex);
     sCallback = nullptr;
     return Void();
 }
diff --git a/gnss/2.0/default/GnssMeasurement.h b/gnss/2.0/default/GnssMeasurement.h
index d8ffd59..73eaa13 100644
--- a/gnss/2.0/default/GnssMeasurement.h
+++ b/gnss/2.0/default/GnssMeasurement.h
@@ -61,10 +61,14 @@
     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;
 };