diff --git a/src/net_builtin.h b/src/net_builtin.h
index 618ce991..e6e625d7 100644
--- a/src/net_builtin.h
+++ b/src/net_builtin.h
@@ -6,6 +6,7 @@
 
 #if defined(MG_ENABLE_TCPIP) && MG_ENABLE_TCPIP
 struct mg_tcpip_if;  // Mongoose TCP/IP network interface
+#define MG_TCPIP_IFACE(mgr_) ((struct mg_tcpip_if *) (mgr_)->priv)
 
 struct mg_tcpip_driver {
   bool (*init)(struct mg_tcpip_if *);                         // Init driver