diff --git a/internal/impl/codec_map.go b/internal/impl/codec_map.go
index fb35f0b..229c698 100644
--- a/internal/impl/codec_map.go
+++ b/internal/impl/codec_map.go
@@ -94,7 +94,7 @@
 		return 0
 	}
 	n := 0
-	iter := mapRange(mapv)
+	iter := mapv.MapRange()
 	for iter.Next() {
 		key := mapi.conv.keyConv.PBValueOf(iter.Key()).MapKey()
 		keySize := mapi.keyFuncs.size(key.Value(), mapKeyTagSize, opts)
@@ -281,7 +281,7 @@
 	if opts.Deterministic() {
 		return appendMapDeterministic(b, mapv, mapi, f, opts)
 	}
-	iter := mapRange(mapv)
+	iter := mapv.MapRange()
 	for iter.Next() {
 		var err error
 		b = protowire.AppendVarint(b, f.wiretag)
@@ -328,7 +328,7 @@
 		if !mi.needsInitCheck {
 			return nil
 		}
-		iter := mapRange(mapv)
+		iter := mapv.MapRange()
 		for iter.Next() {
 			val := pointerOfValue(iter.Value())
 			if err := mi.checkInitializedPointer(val); err != nil {
@@ -336,7 +336,7 @@
 			}
 		}
 	} else {
-		iter := mapRange(mapv)
+		iter := mapv.MapRange()
 		for iter.Next() {
 			val := mapi.conv.valConv.PBValueOf(iter.Value())
 			if err := mapi.valFuncs.isInit(val); err != nil {
@@ -356,7 +356,7 @@
 	if dstm.IsNil() {
 		dstm.Set(reflect.MakeMap(f.ft))
 	}
-	iter := mapRange(srcm)
+	iter := srcm.MapRange()
 	for iter.Next() {
 		dstm.SetMapIndex(iter.Key(), iter.Value())
 	}
@@ -371,7 +371,7 @@
 	if dstm.IsNil() {
 		dstm.Set(reflect.MakeMap(f.ft))
 	}
-	iter := mapRange(srcm)
+	iter := srcm.MapRange()
 	for iter.Next() {
 		dstm.SetMapIndex(iter.Key(), reflect.ValueOf(append(emptyBuf[:], iter.Value().Bytes()...)))
 	}
@@ -386,7 +386,7 @@
 	if dstm.IsNil() {
 		dstm.Set(reflect.MakeMap(f.ft))
 	}
-	iter := mapRange(srcm)
+	iter := srcm.MapRange()
 	for iter.Next() {
 		val := reflect.New(f.ft.Elem().Elem())
 		if f.mi != nil {
diff --git a/internal/impl/codec_map_go111.go b/internal/impl/codec_map_go111.go
deleted file mode 100644
index 4b15493..0000000
--- a/internal/impl/codec_map_go111.go
+++ /dev/null
@@ -1,38 +0,0 @@
-// 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.
-
-//go:build !go1.12
-// +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])
-}
diff --git a/internal/impl/codec_map_go112.go b/internal/impl/codec_map_go112.go
deleted file mode 100644
index 0b31b66..0000000
--- a/internal/impl/codec_map_go112.go
+++ /dev/null
@@ -1,12 +0,0 @@
-// 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.
-
-//go:build go1.12
-// +build go1.12
-
-package impl
-
-import "reflect"
-
-func mapRange(v reflect.Value) *reflect.MapIter { return v.MapRange() }
diff --git a/internal/impl/convert_map.go b/internal/impl/convert_map.go
index 304244a..e4580b3 100644
--- a/internal/impl/convert_map.go
+++ b/internal/impl/convert_map.go
@@ -101,7 +101,7 @@
 	return v
 }
 func (ms *mapReflect) Range(f func(protoreflect.MapKey, protoreflect.Value) bool) {
-	iter := mapRange(ms.v)
+	iter := ms.v.MapRange()
 	for iter.Next() {
 		k := ms.keyConv.PBValueOf(iter.Key()).MapKey()
 		v := ms.valConv.PBValueOf(iter.Value())