diff --git a/vendor/google.golang.org/protobuf/internal/impl/codec_map_go111.go b/vendor/google.golang.org/protobuf/internal/impl/codec_map_go111.go
new file mode 100644
index 0000000..2706bb6
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/impl/codec_map_go111.go
@@ -0,0 +1,37 @@
+// Copyright 2019 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 !go1.12
+
+package impl
+
+import "reflect"
+
+type mapIter struct {
+	v    reflect.Value
+	keys []reflect.Value
+}
+
+// mapRange provides a less-efficient equivalent to
+// the Go 1.12 reflect.Value.MapRange method.
+func mapRange(v reflect.Value) *mapIter {
+	return &mapIter{v: v}
+}
+
+func (i *mapIter) Next() bool {
+	if i.keys == nil {
+		i.keys = i.v.MapKeys()
+	} else {
+		i.keys = i.keys[1:]
+	}
+	return len(i.keys) > 0
+}
+
+func (i *mapIter) Key() reflect.Value {
+	return i.keys[0]
+}
+
+func (i *mapIter) Value() reflect.Value {
+	return i.v.MapIndex(i.keys[0])
+}