diff --git a/unum/vendor/golang.org/x/net/icmp/ipv6.go b/unum/vendor/golang.org/x/net/icmp/ipv6.go
new file mode 100644
index 0000000..2e8cfeb
--- /dev/null
+++ b/unum/vendor/golang.org/x/net/icmp/ipv6.go
@@ -0,0 +1,23 @@
+// Copyright 2013 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 icmp
+
+import (
+	"net"
+
+	"golang.org/x/net/internal/iana"
+)
+
+const ipv6PseudoHeaderLen = 2*net.IPv6len + 8
+
+// IPv6PseudoHeader returns an IPv6 pseudo header for checksum
+// calculation.
+func IPv6PseudoHeader(src, dst net.IP) []byte {
+	b := make([]byte, ipv6PseudoHeaderLen)
+	copy(b, src.To16())
+	copy(b[net.IPv6len:], dst.To16())
+	b[len(b)-1] = byte(iana.ProtocolIPv6ICMP)
+	return b
+}