diff --git a/internal/impl/decode.go b/internal/impl/decode.go
index 3e26223..50b0cf1 100644
--- a/internal/impl/decode.go
+++ b/internal/impl/decode.go
@@ -24,7 +24,8 @@
 	// Keep this field's type identical to (proto.UnmarshalOptions).Resolver
 	// to avoid a type conversion on assignment.
 	resolver interface {
-		preg.ExtensionTypeResolver
+		FindExtensionByName(field pref.FullName) (pref.ExtensionType, error)
+		FindExtensionByNumber(message pref.FullName, field pref.FieldNumber) (pref.ExtensionType, error)
 	}
 }
 
diff --git a/internal/testprotos/irregular/irregular.go b/internal/testprotos/irregular/irregular.go
index 4240124..da5c396 100644
--- a/internal/testprotos/irregular/irregular.go
+++ b/internal/testprotos/irregular/irregular.go
@@ -8,6 +8,7 @@
 	"google.golang.org/protobuf/encoding/prototext"
 	"google.golang.org/protobuf/reflect/protodesc"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/runtime/protoiface"
 
 	"google.golang.org/protobuf/types/descriptorpb"
 )
@@ -26,6 +27,7 @@
 func (m *message) New() pref.Message                  { return &message{} }
 func (m *message) Zero() pref.Message                 { return (*message)(nil) }
 func (m *message) Interface() pref.ProtoMessage       { return (*IrregularMessage)(m) }
+func (m *message) ProtoMethods() *protoiface.Methods  { return nil }
 
 var fieldDescS = fileDesc.Messages().Get(0).Fields().Get(0)
 
diff --git a/proto/decode.go b/proto/decode.go
index 03ea7ec..cea434d 100644
--- a/proto/decode.go
+++ b/proto/decode.go
@@ -38,7 +38,8 @@
 	// Resolver is used for looking up types when unmarshaling extension fields.
 	// If nil, this defaults to using protoregistry.GlobalTypes.
 	Resolver interface {
-		protoregistry.ExtensionTypeResolver
+		FindExtensionByName(field protoreflect.FullName) (protoreflect.ExtensionType, error)
+		FindExtensionByNumber(message protoreflect.FullName, field protoreflect.FieldNumber) (protoreflect.ExtensionType, error)
 	}
 }
 
diff --git a/proto/proto_methods.go b/proto/proto_methods.go
index 86dde4a..d8dd604 100644
--- a/proto/proto_methods.go
+++ b/proto/proto_methods.go
@@ -15,8 +15,5 @@
 const hasProtoMethods = true
 
 func protoMethods(m protoreflect.Message) *protoiface.Methods {
-	if x, ok := m.(protoiface.Methoder); ok {
-		return x.ProtoMethods()
-	}
-	return nil
+	return m.ProtoMethods()
 }
diff --git a/reflect/protoreflect/methods.go b/reflect/protoreflect/methods.go
new file mode 100644
index 0000000..171ed6f
--- /dev/null
+++ b/reflect/protoreflect/methods.go
@@ -0,0 +1,44 @@
+// Copyright 2020 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 protoreflect
+
+import (
+	"google.golang.org/protobuf/internal/pragma"
+)
+
+// The following types are used by the fast-path Message.ProtoMethods method.
+//
+// To avoid polluting the public protoreflect API with types used only by
+// low-level implementations, the canonical definitions of these types are
+// in the runtime/protoiface package. The definitions here and in protoiface
+// must be kept in sync.
+type (
+	methods = struct {
+		pragma.NoUnkeyedLiterals
+		Flags         supportFlags
+		Size          func(m Message, opts marshalOptions) int
+		MarshalAppend func(b []byte, m Message, opts marshalOptions) ([]byte, error)
+		Unmarshal     func(b []byte, m Message, opts unmarshalOptions) error
+		IsInitialized func(m Message) error
+	}
+	supportFlags   = uint64
+	marshalOptions = struct {
+		pragma.NoUnkeyedLiterals
+		AllowPartial  bool
+		Deterministic bool
+		UseCachedSize bool
+	}
+
+	unmarshalOptions = struct {
+		pragma.NoUnkeyedLiterals
+		Merge          bool
+		AllowPartial   bool
+		DiscardUnknown bool
+		Resolver       interface {
+			FindExtensionByName(field FullName) (ExtensionType, error)
+			FindExtensionByNumber(message FullName, field FieldNumber) (ExtensionType, error)
+		}
+	}
+)
diff --git a/reflect/protoreflect/value.go b/reflect/protoreflect/value.go
index e37a233..c7da263 100644
--- a/reflect/protoreflect/value.go
+++ b/reflect/protoreflect/value.go
@@ -150,6 +150,14 @@
 	// be preserved in marshaling or other operations.
 	IsValid() bool
 
+	// ProtoMethods returns optional fast-path implementions of various operations.
+	// This method may return nil.
+	//
+	// The returned methods type is identical to
+	// "google.golang.org/protobuf/runtime/protoiface".Methods.
+	// Consult the protoiface package documentation for details.
+	ProtoMethods() *methods
+
 	// TODO: Add method to retrieve ExtensionType by FieldNumber?
 }
 
diff --git a/runtime/protoiface/methods.go b/runtime/protoiface/methods.go
index b7ba129..4b9bb92 100644
--- a/runtime/protoiface/methods.go
+++ b/runtime/protoiface/methods.go
@@ -12,18 +12,10 @@
 import (
 	"google.golang.org/protobuf/internal/pragma"
 	"google.golang.org/protobuf/reflect/protoreflect"
-	"google.golang.org/protobuf/reflect/protoregistry"
 )
 
-// Methoder is an optional interface implemented by protoreflect.Message to
-// provide fast-path implementations of various operations.
-// The returned Methods struct must not be mutated.
-type Methoder interface {
-	ProtoMethods() *Methods // may return nil
-}
-
 // Methods is a set of optional fast-path implementations of various operations.
-type Methods struct {
+type Methods = struct {
 	pragma.NoUnkeyedLiterals
 
 	// Flags indicate support for optional features.
@@ -46,7 +38,7 @@
 	IsInitialized func(m protoreflect.Message) error
 }
 
-type SupportFlags uint64
+type SupportFlags = uint64
 
 const (
 	// SupportMarshalDeterministic reports whether MarshalOptions.Deterministic is supported.
@@ -59,7 +51,7 @@
 // MarshalOptions configure the marshaler.
 //
 // This type is identical to the one in package proto.
-type MarshalOptions struct {
+type MarshalOptions = struct {
 	pragma.NoUnkeyedLiterals
 
 	AllowPartial  bool // must be treated as true by method implementations
@@ -70,13 +62,14 @@
 // UnmarshalOptions configures the unmarshaler.
 //
 // This type is identical to the one in package proto.
-type UnmarshalOptions struct {
+type UnmarshalOptions = struct {
 	pragma.NoUnkeyedLiterals
 
 	Merge          bool // must be treated as true by method implementations
 	AllowPartial   bool // must be treated as true by method implementations
 	DiscardUnknown bool
 	Resolver       interface {
-		protoregistry.ExtensionTypeResolver
+		FindExtensionByName(field protoreflect.FullName) (protoreflect.ExtensionType, error)
+		FindExtensionByNumber(message protoreflect.FullName, field protoreflect.FieldNumber) (protoreflect.ExtensionType, error)
 	}
 }
diff --git a/types/dynamicpb/dynamic.go b/types/dynamicpb/dynamic.go
index 828a2be..4109128 100644
--- a/types/dynamicpb/dynamic.go
+++ b/types/dynamicpb/dynamic.go
@@ -10,7 +10,8 @@
 
 	"google.golang.org/protobuf/internal/errors"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
-	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	"google.golang.org/protobuf/runtime/protoiface"
+	"google.golang.org/protobuf/runtime/protoimpl"
 )
 
 // A Message is a dynamically constructed protocol buffer message.
@@ -76,6 +77,12 @@
 	return m
 }
 
+// ProtoMethods is an internal detail of the protoreflect.Message interface.
+// Users should never call this directly.
+func (m *Message) ProtoMethods() *protoiface.Methods {
+	return nil
+}
+
 // Range visits every populated field in undefined order.
 // See protoreflect.Message for details.
 func (m *Message) Range(f func(pref.FieldDescriptor, pref.Value) bool) {