diff --git a/route/empty.s b/route/empty.s
index bff0231..90ab4ca 100644
--- a/route/empty.s
+++ b/route/empty.s
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build darwin && go1.12
 // +build darwin,go1.12
 
 // This exists solely so we can linkname in symbols from syscall.