diff --git a/src/pkg/syscall/route_bsd.go b/src/pkg/syscall/route_bsd.go
index 22a0a4f..f6b124b 100644
--- a/src/pkg/syscall/route_bsd.go
+++ b/src/pkg/syscall/route_bsd.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build darwin freebsd openbsd
+
 // Routing sockets and messages
 
 package syscall