diff --git a/inet/netinet/in.h b/inet/netinet/in.h
index 858652cc37..60deab2f99 100644
--- a/inet/netinet/in.h
+++ b/inet/netinet/in.h
@@ -81,6 +81,8 @@ enum
 #define IPPROTO_PIM		IPPROTO_PIM
     IPPROTO_COMP = 108,	   /* Compression Header Protocol.  */
 #define IPPROTO_COMP		IPPROTO_COMP
+    IPPROTO_L2TP = 115,	   /* Layer 2 Tunnelling Protocol.  */
+#define IPPROTO_L2TP		IPPROTO_L2TP
     IPPROTO_SCTP = 132,	   /* Stream Control Transmission Protocol.  */
 #define IPPROTO_SCTP		IPPROTO_SCTP
     IPPROTO_UDPLITE = 136, /* UDP-Lite protocol.  */