diff --git a/src/os/sys_darwin.go b/src/os/sys_darwin.go
deleted file mode 100644
index 11d678ef18d25382b2977e2d562f5188ee8ddd07..0000000000000000000000000000000000000000
--- a/src/os/sys_darwin.go
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package os
-
-// supportsCloseOnExec reports whether the platform supports the
-// O_CLOEXEC flag.
-// The O_CLOEXEC flag was introduced in OS X 10.7 (Darwin 11.0.0).
-// See http://support.apple.com/kb/HT1633.
-const supportsCloseOnExec = true
diff --git a/src/os/sys_freebsd.go b/src/os/sys_freebsd.go
deleted file mode 100644
index 3ec49faedf10e92fc3d18fe0a4720aa12c9a72ec..0000000000000000000000000000000000000000
--- a/src/os/sys_freebsd.go
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package os
-
-// supportsCloseOnExec reports whether the platform supports the
-// O_CLOEXEC flag.
-// The O_CLOEXEC flag was introduced in FreeBSD 8.3.
-const supportsCloseOnExec bool = true
diff --git a/src/os/sys_unix.go b/src/os/sys_unix.go
index 39c20dc739523c3f0ca2b713ea28710db41dc558..87f36cfa4af2f1f77364fe41bd10c3c1824e648f 100644
--- a/src/os/sys_unix.go
+++ b/src/os/sys_unix.go
@@ -2,10 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build dragonfly linux netbsd openbsd solaris
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
 
 package os
 
 // supportsCloseOnExec reports whether the platform supports the
 // O_CLOEXEC flag.
+// On Darwin, the O_CLOEXEC flag was introduced in OS X 10.7 (Darwin 11.0.0).
+// See http://support.apple.com/kb/HT1633.
+// On FreeBSD, the O_CLOEXEC flag was introduced in version 8.3.
 const supportsCloseOnExec = true