diff --git a/src/pkg/syscall/passfd_test.go b/src/pkg/syscall/passfd_test.go
index 20ef39ecaab..71a4a495f0c 100644
--- a/src/pkg/syscall/passfd_test.go
+++ b/src/pkg/syscall/passfd_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build linux darwin
+// +build linux darwin freebsd netbsd
 
 package syscall_test
 
diff --git a/src/pkg/syscall/sockcmsg_unix.go b/src/pkg/syscall/sockcmsg_unix.go
index 7d9a6ee8150..3af3068fd93 100644
--- a/src/pkg/syscall/sockcmsg_unix.go
+++ b/src/pkg/syscall/sockcmsg_unix.go
@@ -37,7 +37,7 @@ func CmsgSpace(datalen int) int {
 }
 
 func cmsgData(h *Cmsghdr) unsafe.Pointer {
-	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + SizeofCmsghdr)
+	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
 }
 
 // SocketControlMessage represents a socket control message.