diff --git a/real_system_state.h b/real_system_state.h
index 18a0d98..d6a9a95 100644
--- a/real_system_state.h
+++ b/real_system_state.h
@@ -122,8 +122,10 @@
   inline bool system_rebooted() override { return system_rebooted_; }
 
  private:
-  // Real DBus proxies using the DBus connection.
+#if USE_LIBCROS
+  // LibCros proxy using the DBus connection.
   LibCrosProxy libcros_proxy_;
+#endif  // USE_LIBCROS
 
   // Interface for the power manager.
   std::unique_ptr<PowerManagerInterface> power_manager_;