diff --git a/ipv4/helper_posix.go b/ipv4/helper_posix.go
new file mode 100644
index 0000000..0adb3e1
--- /dev/null
+++ b/ipv4/helper_posix.go
@@ -0,0 +1,42 @@
+// Copyright 2012 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.
+
+// +build darwin freebsd linux netbsd openbsd windows
+
+package ipv4
+
+import (
+	"bytes"
+	"net"
+	"syscall"
+)
+
+func setSyscallIPMreq(mreq *syscall.IPMreq, ifi *net.Interface) error {
+	if ifi == nil {
+		return nil
+	}
+	ifat, err := ifi.Addrs()
+	if err != nil {
+		return err
+	}
+	for _, ifa := range ifat {
+		switch v := ifa.(type) {
+		case *net.IPAddr:
+			if a := v.IP.To4(); a != nil {
+				copy(mreq.Interface[:], a)
+				goto done
+			}
+		case *net.IPNet:
+			if a := v.IP.To4(); a != nil {
+				copy(mreq.Interface[:], a)
+				goto done
+			}
+		}
+	}
+done:
+	if bytes.Equal(mreq.Multiaddr[:], net.IPv4zero.To4()) {
+		return errNoSuchMulticastInterface
+	}
+	return nil
+}