diff --git a/src/yggdrasil/tun_bsd.go b/src/yggdrasil/tun_bsd.go
index d441829..84a9d3c 100644
--- a/src/yggdrasil/tun_bsd.go
+++ b/src/yggdrasil/tun_bsd.go
@@ -1,3 +1,5 @@
+// +build openbsd freebsd
+
 package yggdrasil
 
 import "os/exec"