diff --git a/include/netinet/tcp.h b/include/netinet/tcp.h
index 4d20936a0b53d0b344afc30655355e66b6684ab6..94a4f8e20b8fcb5277af277713c8a010c61d72b6 100644
--- a/include/netinet/tcp.h
+++ b/include/netinet/tcp.h
@@ -220,6 +220,14 @@ struct tcp_md5sig {
 	uint8_t tcpm_key[TCP_MD5SIG_MAXKEYLEN];
 };
 
+struct tcp_diag_md5sig {
+	uint8_t tcpm_family;
+	uint8_t tcpm_prefixlen;
+	uint16_t tcpm_keylen;
+	uint32_t tcpm_addr[4];
+	uint8_t tcpm_key[TCP_MD5SIG_MAXKEYLEN];
+};
+
 struct tcp_repair_window {
 	uint32_t snd_wl1;
 	uint32_t snd_wnd;