diff --git a/src/pkg/os/signal/signal.go b/src/pkg/os/signal/signal.go
index 520f3f8a9e..bbf9d17289 100644
--- a/src/pkg/os/signal/signal.go
+++ b/src/pkg/os/signal/signal.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 linux netbsd openbsd windows
+
 // Package signal implements operating system-independent signal handling.
 package signal
 
diff --git a/src/pkg/os/signal/signal_test.go b/src/pkg/os/signal/signal_test.go
index 00eb29578f..8445a78460 100644
--- a/src/pkg/os/signal/signal_test.go
+++ b/src/pkg/os/signal/signal_test.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 linux netbsd openbsd windows
+
 package signal
 
 import (