diff --git a/base/include/hidl/HidlInternal.h b/base/include/hidl/HidlInternal.h
index 3cd246a..3d1a444 100644
--- a/base/include/hidl/HidlInternal.h
+++ b/base/include/hidl/HidlInternal.h
@@ -201,7 +201,10 @@
     // A list of registered instrumentation callbacks.
     std::vector<InstrumentationCallback> mInstrumentationCallbacks;
     // Flag whether to enable instrumentation.
-    bool mEnableInstrumentation;
+    union {
+        bool mEnableInstrumentation;
+        void* mReserved0;
+    };
     // Prefix to lookup the instrumentation libraries.
     std::string mInstrumentationLibPackage;
     // Used for dlsym to load the profiling method for given interface.
@@ -209,6 +212,12 @@
 
 };
 
+#ifdef __LP64__
+static_assert(sizeof(HidlInstrumentor) == 88, "HidlInstrumentor size frozen by prebuilts");
+#else
+static_assert(sizeof(HidlInstrumentor) == 44, "HidlInstrumentor size frozen by prebuilts");
+#endif
+
 }  // namespace details
 }  // namespace hardware
 }  // namespace android