diff --git a/daemon/face/multicast-ethernet-transport.hpp b/daemon/face/multicast-ethernet-transport.hpp
index 6d25b41..6ef893b 100644
--- a/daemon/face/multicast-ethernet-transport.hpp
+++ b/daemon/face/multicast-ethernet-transport.hpp
@@ -51,6 +51,11 @@
    */
   bool
   joinMulticastGroup();
+
+private:
+#if defined(__linux__)
+  int m_interfaceIndex;
+#endif
 };
 
 } // namespace face