diff -uNr transmission-2.94/third-party/libnatpmp/natpmp.h transmission-2.94.mod/third-party/libnatpmp/natpmp.h
--- transmission-2.94/third-party/libnatpmp/natpmp.h	2018-05-01 20:18:29.000000000 +0300
+++ transmission-2.94.mod/third-party/libnatpmp/natpmp.h	2018-10-06 01:38:32.814708049 +0300
@@ -51,6 +51,8 @@
 #include <netinet/in.h>
 #endif
 
+#include <arpa/inet.h>
+
 typedef struct {
 	int s;	/* socket */
 	in_addr_t gateway;	/* default gateway (IPv4) */