diff --git a/vendor/github.com/xdg/stringprep/map.go b/vendor/github.com/xdg/stringprep/map.go
new file mode 100644
index 0000000..e56a0dd
--- /dev/null
+++ b/vendor/github.com/xdg/stringprep/map.go
@@ -0,0 +1,21 @@
+// Copyright 2018 by David A. Golden. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
+package stringprep
+
+// Mapping represents a stringprep mapping, from a single rune to zero or more
+// runes.
+type Mapping map[rune][]rune
+
+// Map maps a rune to a (possibly empty) rune slice via a stringprep Mapping.
+// The ok return value is false if the rune was not found.
+func (m Mapping) Map(r rune) (replacement []rune, ok bool) {
+	rs, ok := m[r]
+	if !ok {
+		return nil, false
+	}
+	return rs, true
+}