diff --git a/src/tun.c b/src/tun.c
index 55de5b4..ba2be65 100644
--- a/src/tun.c
+++ b/src/tun.c
@@ -227,7 +227,7 @@ tun_setip(const char *ip, int netbits)
 }
 
 int 
-tun_setmtu(const size_t mtu)
+tun_setmtu(const unsigned mtu)
 {
 	char cmdline[512];
 
diff --git a/src/tun.h b/src/tun.h
index 2f1faa4..3f99dc0 100644
--- a/src/tun.h
+++ b/src/tun.h
@@ -22,6 +22,6 @@ void close_tun(int);
 int write_tun(int, char *, size_t);
 ssize_t read_tun(int, char *, size_t);
 int tun_setip(const char *, int);
-int tun_setmtu(const size_t);
+int tun_setmtu(const unsigned);
 
 #endif /* _TUN_H_ */