diff --git a/internal/cmd/generate-protos/main.go b/internal/cmd/generate-protos/main.go
index 0f96484..01b0fe6 100644
--- a/internal/cmd/generate-protos/main.go
+++ b/internal/cmd/generate-protos/main.go
@@ -131,7 +131,7 @@
 			"internal/testprotos/irregular/irregular.proto": true,
 		}},
 	}
-	excludeRx := regexp.MustCompile(`legacy/proto[23]_[0-9]{8}_[0-9a-f]{8}/`)
+	excludeRx := regexp.MustCompile(`legacy/.*/`)
 	for _, d := range dirs {
 		subDirs := map[string]bool{}
 
diff --git a/internal/testprotos/legacy/bug1052/bug1052.pb.go b/internal/testprotos/legacy/bug1052/bug1052.pb.go
new file mode 100644
index 0000000..174e9d0
--- /dev/null
+++ b/internal/testprotos/legacy/bug1052/bug1052.pb.go
@@ -0,0 +1,99 @@
+// 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.
+
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// source: internal/testprotos/legacy/bug1052/bug1052.proto
+
+package bug1052
+
+import (
+	fmt "fmt"
+	math "math"
+
+	proto "github.com/golang/protobuf/proto"
+	descriptor "github.com/golang/protobuf/protoc-gen-go/descriptor"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.ProtoPackageIsVersion3 // please upgrade the proto package
+
+type Enum int32
+
+const (
+	Enum_ZERO Enum = 0
+)
+
+var Enum_name = map[int32]string{
+	0: "ZERO",
+}
+
+var Enum_value = map[string]int32{
+	"ZERO": 0,
+}
+
+func (x Enum) Enum() *Enum {
+	p := new(Enum)
+	*p = x
+	return p
+}
+
+func (x Enum) String() string {
+	return proto.EnumName(Enum_name, int32(x))
+}
+
+func (x *Enum) UnmarshalJSON(data []byte) error {
+	value, err := proto.UnmarshalJSONEnum(Enum_value, data, "Enum")
+	if err != nil {
+		return err
+	}
+	*x = Enum(value)
+	return nil
+}
+
+func (Enum) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_2d34d4f47c51af27, []int{0}
+}
+
+var E_ExtensionEnum = &proto.ExtensionDesc{
+	ExtendedType:  (*descriptor.MethodOptions)(nil),
+	ExtensionType: (*Enum)(nil),
+	Field:         5000,
+	Name:          "goproto.proto.legacy.extension_enum",
+	Tag:           "varint,5000,opt,name=extension_enum,enum=goproto.proto.legacy.Enum",
+	Filename:      "internal/testprotos/legacy/bug1052/bug1052.proto",
+}
+
+func init() {
+	proto.RegisterEnum("goproto.proto.legacy.Enum", Enum_name, Enum_value)
+	proto.RegisterExtension(E_ExtensionEnum)
+}
+
+func init() {
+	proto.RegisterFile("internal/testprotos/legacy/bug1052/bug1052.proto", fileDescriptor_2d34d4f47c51af27)
+}
+
+var fileDescriptor_2d34d4f47c51af27 = []byte{
+	// 200 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0x32, 0xc8, 0xcc, 0x2b, 0x49,
+	0x2d, 0xca, 0x4b, 0xcc, 0xd1, 0x2f, 0x49, 0x2d, 0x2e, 0x29, 0x28, 0xca, 0x2f, 0xc9, 0x2f, 0xd6,
+	0xcf, 0x49, 0x4d, 0x4f, 0x4c, 0xae, 0xd4, 0x4f, 0x2a, 0x4d, 0x37, 0x34, 0x30, 0x35, 0x82, 0xd1,
+	0x7a, 0x60, 0x59, 0x21, 0x91, 0xf4, 0x7c, 0x30, 0x03, 0xc2, 0xd5, 0x83, 0xa8, 0x95, 0x52, 0x48,
+	0xcf, 0xcf, 0x4f, 0xcf, 0x49, 0xd5, 0x07, 0x0b, 0x26, 0x95, 0xa6, 0xe9, 0xa7, 0xa4, 0x16, 0x27,
+	0x17, 0x65, 0x16, 0x94, 0xe4, 0x17, 0x41, 0x14, 0x6a, 0x09, 0x70, 0xb1, 0xb8, 0xe6, 0x95, 0xe6,
+	0x0a, 0x71, 0x70, 0xb1, 0x44, 0xb9, 0x06, 0xf9, 0x0b, 0x30, 0x58, 0x25, 0x71, 0xf1, 0xa5, 0x56,
+	0x94, 0xa4, 0xe6, 0x15, 0x67, 0xe6, 0xe7, 0xc5, 0xa7, 0x82, 0xe4, 0xe4, 0xf4, 0x20, 0xc6, 0xe8,
+	0xc1, 0x8c, 0xd1, 0xf3, 0x4d, 0x2d, 0xc9, 0xc8, 0x4f, 0xf1, 0x2f, 0x28, 0xc9, 0xcc, 0xcf, 0x2b,
+	0x96, 0xe8, 0x50, 0x57, 0x60, 0xd4, 0xe0, 0x33, 0x92, 0xd2, 0xc3, 0xe6, 0x06, 0x3d, 0x90, 0xf1,
+	0x41, 0xbc, 0x70, 0x23, 0x41, 0x5c, 0x27, 0xfb, 0x28, 0x5b, 0xa8, 0x91, 0xe9, 0xf9, 0x39, 0x89,
+	0x79, 0xe9, 0x7a, 0xf9, 0x45, 0xe9, 0x08, 0x47, 0x12, 0xf6, 0x3c, 0x20, 0x00, 0x00, 0xff, 0xff,
+	0x1d, 0x9e, 0x09, 0x6e, 0x21, 0x01, 0x00, 0x00,
+}
diff --git a/internal/testprotos/legacy/bug1052/bug1052.proto b/internal/testprotos/legacy/bug1052/bug1052.proto
new file mode 100644
index 0000000..adcb118
--- /dev/null
+++ b/internal/testprotos/legacy/bug1052/bug1052.proto
@@ -0,0 +1,26 @@
+// 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.
+
+// This file exercises a deadlock in registation of legacy extensions:
+// https://github.com/golang/protobuf/issues/1052
+//
+// The corresponding .pb.go file was generated with protoc 3.11.3 and
+// protoc-gen-go 1.3.3.
+
+syntax = "proto2";
+
+package goproto.proto.legacy;
+
+import "google/protobuf/descriptor.proto";
+
+option go_package = "google.golang.org/protobuf/internal/testprotos/legacy/bug1052";
+
+enum Enum {
+  ZERO = 0;
+}
+
+extend google.protobuf.MethodOptions {
+  optional Enum extension_enum = 5000;
+}
+
diff --git a/internal/testprotos/legacy/bug1052/bug1052_test.go b/internal/testprotos/legacy/bug1052/bug1052_test.go
new file mode 100644
index 0000000..eb0881c
--- /dev/null
+++ b/internal/testprotos/legacy/bug1052/bug1052_test.go
@@ -0,0 +1,9 @@
+// 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 bug1052_test
+
+import (
+	_ "google.golang.org/protobuf/internal/testprotos/legacy/bug1052"
+)
diff --git a/reflect/protoregistry/registry.go b/reflect/protoregistry/registry.go
index 4fc8158..43f16c6 100644
--- a/reflect/protoregistry/registry.go
+++ b/reflect/protoregistry/registry.go
@@ -414,12 +414,16 @@
 //
 // If a naming conflict occurs, the type is not registered and an error is returned.
 func (r *Types) RegisterMessage(mt protoreflect.MessageType) error {
+	// Under rare circumstances getting the descriptor might recursively
+	// examine the registry, so fetch it before locking.
+	md := mt.Descriptor()
+
 	if r == GlobalTypes {
 		globalMutex.Lock()
 		defer globalMutex.Unlock()
 	}
 
-	if err := r.register("message", mt.Descriptor(), mt); err != nil {
+	if err := r.register("message", md, mt); err != nil {
 		return err
 	}
 	r.numMessages++
@@ -430,12 +434,16 @@
 //
 // If a naming conflict occurs, the type is not registered and an error is returned.
 func (r *Types) RegisterEnum(et protoreflect.EnumType) error {
+	// Under rare circumstances getting the descriptor might recursively
+	// examine the registry, so fetch it before locking.
+	ed := et.Descriptor()
+
 	if r == GlobalTypes {
 		globalMutex.Lock()
 		defer globalMutex.Unlock()
 	}
 
-	if err := r.register("enum", et.Descriptor(), et); err != nil {
+	if err := r.register("enum", ed, et); err != nil {
 		return err
 	}
 	r.numEnums++
@@ -446,12 +454,18 @@
 //
 // If a naming conflict occurs, the type is not registered and an error is returned.
 func (r *Types) RegisterExtension(xt protoreflect.ExtensionType) error {
+	// Under rare circumstances getting the descriptor might recursively
+	// examine the registry, so fetch it before locking.
+	//
+	// A known case where this can happen: Fetching the TypeDescriptor for a
+	// legacy ExtensionDesc can consult the global registry.
+	xd := xt.TypeDescriptor()
+
 	if r == GlobalTypes {
 		globalMutex.Lock()
 		defer globalMutex.Unlock()
 	}
 
-	xd := xt.TypeDescriptor()
 	field := xd.Number()
 	message := xd.ContainingMessage().FullName()
 	if prev := r.extensionsByMessage[message][field]; prev != nil {
@@ -462,7 +476,7 @@
 		}
 	}
 
-	if err := r.register("extension", xt.TypeDescriptor(), xt); err != nil {
+	if err := r.register("extension", xd, xt); err != nil {
 		return err
 	}
 	if r.extensionsByMessage == nil {