diff --git a/src/pkg/runtime/netpoll_stub.c b/src/pkg/runtime/netpoll_stub.c
index 4dba886..db2b1ee 100644
--- a/src/pkg/runtime/netpoll_stub.c
+++ b/src/pkg/runtime/netpoll_stub.c
@@ -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 freebsd linux netbsd openbsd plan9 windows
+
 #include "runtime.h"
 
 // Polls for ready network connections.