diff --git a/src/vnet/devices/tap/tap.h b/src/vnet/devices/tap/tap.h
index 5d087ad..c1ac7a6 100644
--- a/src/vnet/devices/tap/tap.h
+++ b/src/vnet/devices/tap/tap.h
@@ -35,6 +35,7 @@
 #define TAP_FLAG_CSUM_OFFLOAD (1 << 1)
 #define TAP_FLAG_PERSIST (1 << 2)
 #define TAP_FLAG_ATTACH (1 << 3)
+#define TAP_FLAG_TUN (1 << 4)
   u8 *host_namespace;
   u8 *host_if_name;
   mac_address_t host_mac_addr;